Difference between revisions of "John's Linux page"

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Quick jump to: [[#NetBeans|NetBeans]].
 
Quick jump to: [[#NetBeans|NetBeans]].
 +
 +
= References =
 +
 +
== Command-line ==
 +
 +
See [https://zaiste.net/posts/shell-commands-rust/ Shell Commands I Wish I Knew Earlier] for some interesting options.
  
 
= System =
 
= System =
 +
 +
== Reporting system specifications from the command-line ==
 +
 +
Try any of these:
 +
 +
# neofetch
 +
# inxi
 +
# hwinfo --short
 +
 +
You may need to install the relevant package.
  
 
== Determining which Debian/Ubuntu release your are running ==
 
== Determining which Debian/Ubuntu release your are running ==
Line 30: Line 46:
  
 
  $ uname -a
 
  $ uname -a
 +
 +
== Determining which Linux kernel you are running ==
 +
 +
$ uname -r
  
 
== Configuring system swappiness ==
 
== Configuring system swappiness ==
Line 46: Line 66:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 83: Line 99:
 
  Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5
 
  Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5
  
== Viewing syslog and other logs with KSystemLog ==
+
=== Motherboard info ===
 +
 
 +
# dmidecode -t 2
 +
 
 +
=== CPU info ===
 +
 
 +
# lscpu
 +
 
 +
or:
 +
 
 +
# cat /proc/cpuinfo
  
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
+
=== RAM info ===
  
= Power =
+
# dmidecode --type memory
  
== Reporting on PowerShield DEFENDER UPS status ==
+
=== PCI info ===
  
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
+
# lspci -v
  
$ upsc defender
+
=== Drive info ===
  
E.g.:
+
# cat /proc/partitions
  
jj5@orac:~$ upsc defender
+
and:
Init SSL without certificate database
 
battery.charge: 100
 
battery.voltage: 27.40
 
battery.voltage.high: 26.00
 
battery.voltage.low: 20.80
 
battery.voltage.nominal: 24.0
 
device.type: ups
 
driver.name: blazer_usb
 
driver.parameter.pollinterval: 2
 
driver.parameter.port: auto
 
driver.parameter.synchronous: no
 
driver.version: 2.7.4
 
driver.version.internal: 0.12
 
input.current.nominal: 5.0
 
input.frequency: 50.1
 
input.frequency.nominal: 50
 
input.voltage: 242.6
 
input.voltage.fault: 242.6
 
input.voltage.nominal: 240
 
output.voltage: 242.6
 
ups.beeper.status: disabled
 
ups.delay.shutdown: 30
 
ups.delay.start: 180
 
ups.load: 14
 
ups.productid: 5161
 
ups.status: OL
 
ups.type: offline / line interactive
 
ups.vendorid: 0665
 
  
== Run commands on PowerShield DEFENDER UPS batteries ==
+
# hdparm -I /dev/sda
  
You can run "instant commands" using the '''upscmd''' command.
+
and:
  
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
+
# smartctl --info /dev/sda
  
diligence:/srv/salt/conf/app/defender-1200.sls
+
You can check if a drive is SSD or not with:
  
To see "instant commands" supported by the PowerShield DEFENDER:
+
# cat /sys/block/sde/queue/rotational
  
  $ upscmd -l defender
+
  0=SSD
 +
1=HDD
  
E.g.:
+
== Viewing syslog and other logs with KSystemLog ==
  
jj5@orac:~$ upscmd -l defender
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
Instant commands supported on UPS [defender]:
 
 
beeper.toggle - Toggle the UPS beeper
 
load.off - Turn off the load immediately
 
load.on - Turn on the load immediately
 
shutdown.return - Turn off the load and return when power is back
 
shutdown.stayoff - Turn off the load and remain off
 
shutdown.stop - Stop a shutdown in progress
 
test.battery.start - Start a battery test
 
test.battery.start.deep - Start a deep battery test
 
test.battery.start.quick - Start a quick battery test
 
test.battery.stop - Stop the battery test
 
  
= Environment =
+
= CPU =
  
== Configuring vim as your editor ==
+
== Monitoring CPU clock speed ==
  
Sometimes all you need is:
+
Try something like this:
  
  $ export EDITOR=/usr/bin/vim
+
  $ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
= Power =
  
Other times you need to run
+
== Reporting on PowerShield DEFENDER UPS status ==
  
# update-alternatives --config editor
+
Before running `upsc` ensure service is running:
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
# upsdrvctl start
  
== Configuring your locale ==
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
  
  $ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
  $ upsc defender
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
 
  
= User and group management =
+
E.g.:
  
== Adding a user ==
+
jj5@orac:~$ upsc defender
 +
Init SSL without certificate database
 +
battery.charge: 100
 +
battery.voltage: 27.40
 +
battery.voltage.high: 26.00
 +
battery.voltage.low: 20.80
 +
battery.voltage.nominal: 24.0
 +
device.type: ups
 +
driver.name: blazer_usb
 +
driver.parameter.pollinterval: 2
 +
driver.parameter.port: auto
 +
driver.parameter.synchronous: no
 +
driver.version: 2.7.4
 +
driver.version.internal: 0.12
 +
input.current.nominal: 5.0
 +
input.frequency: 50.1
 +
input.frequency.nominal: 50
 +
input.voltage: 242.6
 +
input.voltage.fault: 242.6
 +
input.voltage.nominal: 240
 +
output.voltage: 242.6
 +
ups.beeper.status: disabled
 +
ups.delay.shutdown: 30
 +
ups.delay.start: 180
 +
ups.load: 14
 +
ups.productid: 5161
 +
ups.status: OL
 +
ups.type: offline / line interactive
 +
ups.vendorid: 0665
  
To add a new user on a linux system:
+
== Run commands on PowerShield DEFENDER UPS batteries ==
  
# useradd username
+
You can run "instant commands" using the '''upscmd''' command.
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
  # adduser username
+
  diligence:/srv/salt/conf/app/defender-1200.sls
  
== Adding a user to a group ==
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
To add an existing user to an existing group:
+
$ upscmd -l defender
  
# gpasswd -a username group
+
E.g.:
  
e.g. to add user 'jj5' to the 'sudo' group:
+
jj5@orac:~$ upscmd -l defender
 +
Instant commands supported on UPS [defender]:
 +
 +
beeper.toggle - Toggle the UPS beeper
 +
load.off - Turn off the load immediately
 +
load.on - Turn on the load immediately
 +
shutdown.return - Turn off the load and return when power is back
 +
shutdown.stayoff - Turn off the load and remain off
 +
shutdown.stop - Stop a shutdown in progress
 +
test.battery.start - Start a battery test
 +
test.battery.start.deep - Start a deep battery test
 +
test.battery.start.quick - Start a quick battery test
 +
test.battery.stop - Stop the battery test
  
# gpasswd -a jj5 sudo
+
= Service management =
  
Alternatively you can use adduser, passing the username and group:
+
== Report running services ==
  
  # adduser username group
+
  # service --status-all
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
= Environment =
  
# adduser sclaughl staff
+
== Configuring vim as your editor ==
  
== Disabling a user account ==
+
Sometimes all you need is:
  
You can disable a user account with:
+
$ export EDITOR=/usr/bin/vim
  
# passwd -l user
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
Note: that's a lower-case L, not a one.
+
Other times you need to run
  
== Enabling a disabled user account ==
+
# update-alternatives --config editor
  
To can re-enable a locked user account with:
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
# passwd -u user
+
== Configuring your locale ==
  
== Finding which user you are logged in as ==
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
To determine which user you are running as enter the command:
+
= User and group management =
  
$ whoami
+
== Adding a user ==
  
== Finding which groups you are a member of ==
+
To add a new user on a linux system:
  
To find which groups you are a member of:
+
# useradd username
 +
# passwd username
  
$ groups
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
or
+
# adduser username
  
$ groups username
+
== Adding a user to a group ==
  
Where 'username' is the username of the user you are querying, e.g.:
+
To add an existing user to an existing group:
  
  $ groups jj5
+
  # gpasswd -a username group
  
== Finding who else is logged in to the system ==
+
e.g. to add user 'jj5' to the 'sudo' group:
  
To see who else is logged in,
+
# gpasswd -a jj5 sudo
  
$ who
+
Alternatively you can use adduser, passing the username and group:
  
== Running a command as a particular user ==
+
# adduser username group
  
To run "svn update" as the user www-data:
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
  $ sudo su -c "svn update" www-data
+
  # adduser sclaughl staff
  
== Reporting user and group info for the current user ==
+
== Disabling a user account ==
  
$ id
+
You can disable a user account with:
  
= Memory management =
+
# passwd -l user
  
== Checking available memory ==
+
Note: that's a lower-case L, not a one.
  
To report memory statistics in megabytes:
+
== Enabling a disabled user account ==
  
$ free -m
+
To can re-enable a locked user account with:
  
== Check for swap thrashing ==
+
# passwd -u user
  
Check your virtual memory status with vmstat:
+
== Finding which user you are logged in as ==
  
$ vmstat
+
To determine which user you are running as enter the command:
  
== Report memory type ==
+
$ whoami
  
Report on RAM DIMMs:
+
== Finding which groups you are a member of ==
  
# dmidecode --type 17
+
To find which groups you are a member of:
  
Report on RAM and CPU cache:
+
$ groups
  
# lshw -short -C memory
+
or
  
Or for more detail:
+
$ groups username
  
# lshw -C memory
+
Where 'username' is the username of the user you are querying, e.g.:
  
= Video/display management =
+
$ groups jj5
  
== Viewing EDID data for attached monitor ==
+
== Finding who else is logged in to the system ==
  
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
+
To see who else is logged in,
  
  $ cd /sys/class/drm
+
  $ who
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
== Running a command as a particular user ==
  
== Using 'top' for dynamic resource usage reporting ==
+
To run "svn update" as the user www-data:
  
To run top:
+
$ sudo su -c "svn update" www-data
  
$ top
+
== Reporting user and group info for the current user ==
  
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
+
$ id
  
To see usage for a specific user run e.g.:
+
= Memory management =
  
$ top -u jj5
+
== Checking available memory ==
  
To see full command-line press 'c'.
+
To report memory statistics in megabytes:
  
When you're in 'top' you can:
+
$ free -m
  
* press '1' (one) to toggle CPU aggregation
+
== Check for swap thrashing ==
* press < and > to change the sort column
 
  
== Changing memory reporting in 'top' ==
+
Check your virtual memory status with vmstat:
  
To run top:
+
$ vmstat
  
$ top
+
== Report memory type ==
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
Report on RAM DIMMs:
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
# dmidecode --type 17
  
Press 'M' to sort by memory utilisation.
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
Press 'm' to switch between various display modes.
+
# lshw -short -C memory
  
== Showing full command-line in 'top' ==
+
Or for more detail:
  
To see the full command-line for processes run with -c:
+
# lshw -C memory
  
$ top -c
+
= Video/display management =
  
== Listing all processes currently running which were started in your current shell session ==
+
== Viewing EDID data for attached monitor ==
  
$ ps -fl
+
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
  
== Killing specific processes ==
+
$ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
+
= Process management =
  
== Run a command for a specified time using timeout ==
+
== Using 'top' for dynamic resource usage reporting ==
  
$ timeout 3 ping jj5.net
+
To run top:
  
= Disk management =
+
$ top
  
== Creating a partition table ==
+
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
  
# parted /dev/xvdf
+
To see usage for a specific user run e.g.:
  
  mktable msdos
+
  $ top -u jj5
  
== Creating a partition ==
+
To see full command-line press 'c'.
  
# parted /dev/xvdf
+
When you're in 'top' you can:
  
u MiB
+
* press '1' (one) to toggle CPU aggregation
mkpart primary 1 100%
+
* press < and > to change the sort column
  
== Creating an ext4 file-system ==
+
== Changing memory reporting in 'top' ==
  
# mkfs.ext4 /dev/xvdf1
+
To run top:
  
== Listing disk drives ==
+
$ top
  
# fdisk -l
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
 +
 
 +
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
(That's an L for "list")
+
Press 'M' to sort by memory utilisation.
  
== Checking available disk space ==
+
Press 'm' to switch between various display modes.
  
$ df -h
+
== Showing full command-line in 'top' ==
  
== Getting disk information ==
+
To see the full command-line for processes run with -c:
  
  # lsblk
+
  $ top -c
  
And
+
== Listing all processes currently running which were started in your current shell session ==
  
  # cat /proc/partitions
+
  $ ps -fl
  
Or the Grand Daddy of them all:
+
== Killing specific processes ==
  
  # lshw -class disk
+
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
(Requires the lshw package.)
+
== Run a command for a specified time using timeout ==
  
== Getting partition UUID and file-system type ==
+
$ timeout 3 ping jj5.net
  
# blkid
+
= Disk management =
  
== Checking for SSD vs magnetic disk ==
+
== Power-off a hard drive ==
  
# cat /sys/block/sda/queue/rotational
+
For instance if it's a USB drive or in a mobile rack and you want to remove it.
  
Will be 0 for SSD and 1 for magnetic.
+
# udisksctl power-off -b /dev/sdi
  
== Monitoring a ZFS server ==
+
== Reporting ext4 file-systems mounted without noatime ==
  
So some commands I run to keep an eye on my new ZFS servers:
+
$ cat /proc/mounts | grep ext | grep -v noatime | sort
  
# top
+
== Creating a partition table ==
# iotop
 
# nethogs
 
# watch free -h
 
# watch slabtop -o
 
# slabtop
 
# watch cat /proc/meminfo
 
# perf top
 
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 
# watch zpool iostat -v
 
# zpool iostat -v 2
 
# watch 'zpool list; echo; zfs list'
 
# watch zfs get compressratio -o all
 
# watch cat /proc/spl/kstat/zfs/arcstats
 
  
If you have a scrub or resilvering in progress you can report on progress with:
+
# parted /dev/xvdf
  
  # watch zpool status -v
+
  mktable msdos
  
You can poke about in internals, e.g.:
+
== Creating a partition ==
  
  # cat /proc/spl/kstat/zfs/arcstats
+
  # parted /dev/xvdf
  
  root@orac:/sys/module/zfs/parameters# tail *
+
  u MiB
 +
mkpart primary 1 100%
  
You can report on property values with e.g.:
+
== Creating an ext4 file-system ==
  
  # zfs get all data
+
  # mkfs.ext4 /dev/xvdf1
  
If you want to get funky:
+
== Listing disk drives ==
  
  # cd /tmp
+
  # fdisk -l
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
(That's an L for "list")
  
root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
== Checking available disk space ==
  
You can report history of a zpool:
+
$ df -h
  
# zpool history $poolname
+
== Getting disk information ==
  
You can get a report on the dedup tables:
+
# lsblk
  
# zpool status -D $poolname
+
And
  
Or more detailed dedup table info:
+
# cat /proc/partitions
  
# zdb -DDD $poolname
+
Or the Grand Daddy of them all:
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
# lshw -class disk
  
{|class="wikitable"
+
(Requires the lshw package.)
! Abbr  !! Description
 
|-
 
| LSIZE  || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== Measure data throughput ==
+
== Getting partition UUID and file-system type ==
  
Use the 'pv' command from the 'pv' package, e.g.:
+
# blkid
  
# cat /dev/sda | pv | cat > /dev/null
+
== Checking for SSD vs magnetic disk ==
  
Or for ZFS:
+
# cat /sys/block/sda/queue/rotational
  
# zfs send data/example | pv | cat > /dev/null
+
Will be 0 for SSD and 1 for magnetic.
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
== Monitoring a ZFS server ==
  
For notes on using smartctl see [https://www.lisenet.com/2014/using-smartctl-smartd-and-hddtemp-on-debian/ Using Smartctl, Smartd and Hddtemp on Debian].
+
So some commands I run to keep an eye on my new ZFS servers:
  
== Report hard disk usage ==
+
# top
 +
# iotop
 +
# nethogs
 +
# watch free -h
 +
# watch slabtop -o
 +
# slabtop
 +
# watch cat /proc/meminfo
 +
# perf top
 +
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 +
# watch zpool iostat -v
 +
# zpool iostat -v 2
 +
# watch 'zpool list; echo; zfs list'
 +
# watch zfs get compressratio -o all
 +
# watch cat /proc/spl/kstat/zfs/arcstats
  
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
+
If you have a scrub or resilvering in progress you can report on progress with:
  
== Report hard disk temperatures ==
+
# watch zpool status -v
  
E.g.
+
You can poke about in internals, e.g.:
  
  # hddtemp /dev/sd[a-e]
+
  # cat /proc/spl/kstat/zfs/arcstats
  
== Burning an ISO image to USB on Mac ==
+
root@orac:/sys/module/zfs/parameters# tail *
  
First insert your USB key and find the appropriate disk with:
+
You can report on property values with e.g.:
  
  # diskutil list
+
  # zfs get all data
  
Then unmount it with:
+
If you want to get funky:
  
  # diskutil unmountDisk /dev/disk4
+
  # cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
Then copy ISO image with 'dd':
+
You can search for ZFS files like e.g. this:
  
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
You can get dd to report progress by sending it the SIGINFO signal:
+
You can report history of a zpool:
  
  # kill -s info 12345
+
  # zpool history $poolname
  
== Listing all ext4 file systems ==
+
You can get a report on the dedup tables:
  
To see a list only of the mounted ext4 file systems:
+
# zpool status -D $poolname
  
# df -t ext4
+
Or more detailed dedup table info:
  
== Report hierarchical file system mount points and mount options ==
+
# zdb -DDD $poolname
  
$ findmnt
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
== Report the mount point for the current working directory ==
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
$ findmnt "$PWD"
+
== How to tell if zfs scrub is running ==
  
= Monitoring disk I/O =
+
You can get the status from the "scan:" line from:
  
There's an app for that! iotop.
+
$ zpool status
  
== Using iotop, top for disks ==
+
== Measure data throughput ==
  
# iotop -oPa
+
Use the 'pv' command from the 'pv' package, e.g.:
  
== Monitor disk I/O for performance issues ==
+
# cat /dev/sda | pv | cat > /dev/null
  
# watch iostat
+
Or for ZFS:
  
Or e.g.
+
# zfs send data/example | pv | cat > /dev/null
  
# watch iostat -xd /dev/sd[abc]
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
Or use groupings like this command for 'tact':
+
For notes on using smartctl see [https://www.lisenet.com/2014/using-smartctl-smartd-and-hddtemp-on-debian/ Using Smartctl, Smartd and Hddtemp on Debian].
  
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
== Report hard disk usage ==
  
= Monitoring a system =
+
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
  
== Simple ZFS monitoring ==
+
== Report hard disk temperatures ==
  
# watch iostat
+
E.g.
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
# hddtemp /dev/sd[a-e]
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
== Burning an ISO image to USB on Mac ==
  
$ cat /sys/class/thermal/thermal_zone*/temp
+
First insert your USB key and find the appropriate disk with:
  
and:
+
# diskutil list
  
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
Then unmount it with:
  
== Monitoring CPU temperature ==
+
# diskutil unmountDisk /dev/disk4
  
$ watch sensors
+
Then copy ISO image with 'dd':
  
== Monitoring HDD temperature ==
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
For e.g. SATA drives sda to sdd:
+
You can get dd to report progress by sending it the SIGINFO signal:
  
  # watch hddtemp /dev/sd[a-d]
+
  # kill -s info 12345
  
= ZFS =
+
== Listing all ext4 file systems ==
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
To see a list only of the mounted ext4 file systems:
  
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
+
# df -t ext4
  
$ cat /proc/spl/kstat/zfs/arcstats
+
== Report hierarchical file system mount points and mount options ==
  
Then:
+
$ findmnt
  
c is the target size of the ARC in bytes
+
== Report the mount point for the current working directory ==
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
= File management =
+
$ findmnt "$PWD"
  
== Listing files by size ==
+
= Monitoring disk I/O =
  
Use capital S for Size:
+
There's an app for that! iotop.
  
$ ls -S
+
== Using iotop, top for disks ==
  
== Listing only directories ==
+
# iotop -oPa
  
$ ls -l | egrep '^d'
+
== Monitor disk I/O for performance issues ==
  
== Listing only files ==
+
# watch iostat
  
$ ls -l | egrep -v '^d'
+
Or e.g.
  
== Listing hidden files ==
+
# watch iostat -xd /dev/sd[abc]
  
$ ls -al .[!.]*
+
Or use groupings like this command for 'tact':
  
== Creating a symbolic link ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
$ ln -s /path/to/target link-name
+
= Monitoring a system =
  
== Creating a hard-link ==
+
== Simple ZFS monitoring ==
  
  $ ln /path/to/target file-name
+
  # watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
== Changing the owner of a file ==
+
= Monitoring temperature =
  
$ chown user:group <files>
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
E.g.
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
$ chown jj5:staff README
+
and:
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
$ chown -R root:root /etc/*
+
== Monitoring CPU temperature ==
  
== Changing file permissions ==
+
$ watch sensors
  
{|class="wikitable"
+
== Monitoring HDD temperature ==
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
For e.g. SATA drives sda to sdd:
|+ Permission codes
+
 
! Read !! Write !! Exectue
+
# watch hddtemp /dev/sd[a-d]
|-
+
 
| r    || w    || x
+
= ZFS =
|-
+
 
| 4    || 2    || 1
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
|}
+
 
 +
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
 +
 
 +
$ cat /proc/spl/kstat/zfs/arcstats
 +
 
 +
Then:
  
{|class="wikitable"
+
c is the target size of the ARC in bytes
|+ Numeric codes
+
c_max is the maximum size of the ARC in bytes
! 0
+
size is the current size of the ARC in bytes
| None
 
|-
 
! 1
 
| Execute
 
|-
 
! 2
 
| Write
 
|-
 
! 3
 
| Write, Execute
 
|-
 
! 4
 
| Read
 
|-
 
! 5
 
| Read, Execute
 
|-
 
! 6
 
| Read, Write
 
|-
 
! 7
 
| Read, Write, Execute
 
|}
 
  
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
+
== Stopping a ZFS scrub in progress ==
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  # zpool scrub -s $pool
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
e.g. for the 'data' pool:
  
  $ chmod 600 my-private-file
+
  # zpool scrub -s data
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
= File management =
  
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
+
== Listing files by size ==
  
$ cp old.conf updated.conf
+
Use capital S for Size:
$ merge -A updated.conf new.conf old.conf
 
  
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
+
$ ls -S
  
The merge program is a part of the RCS package. If you don't have it:
+
== Listing only directories ==
  
  $ sudo apt-get install rcs
+
  $ ls -l | egrep '^d'
  
== Listing open files ==
+
== Listing only files ==
  
Use lsof to list open files. E.g.:
+
$ ls -l | egrep -v '^d'
  
# lsof
+
== Listing hidden files ==
  
See man lsof for options.
+
$ ls -al .[!.]*
  
== List permissions on a whole directory path ==
+
== Creating a symbolic link ==
  
E.g.:
+
$ ln -s /path/to/target link-name
  
$ namei -om /home/jj5/workspace
+
== Creating a hard-link ==
  
Outputs:
+
$ ln /path/to/target file-name
  
f: /home/jj5/workspace/
+
== Changing the owner of a file ==
  drwxr-xr-x root root /
 
  drwxr-xr-x root root home
 
  drwxr-xr-x jj5  jj5  jj5
 
  drwxr-xr-x jj5  jj5  workspace
 
  
== Counting non-blank lines in a file ==
+
$ chown user:group <files>
  
E.g.:
+
E.g.
  
  $ cat foo.c | sed '/^\s*$/d' | wc -l
+
  $ chown jj5:staff README
 +
$ chown root:root *
  
== Cloning one directory to another with rsync ==
+
To apply recursively into sub-directories use -R,
  
E.g.:
+
$ chown -R root:root /etc/*
  
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
+
== Changing file permissions ==
  
== Counting number of files in current directory and all subdirectories ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
$ ls -AlhR . | egrep '^-' | wc -l
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
== Counting number of directories in current directory and all subdirectories ==
+
{|class="wikitable"
 
+
|+ Numeric codes
$ ls -AlhR . | egrep '^d' | wc -l
+
! 0
 
+
| None
== Getting the status of a 'dd' process ==
+
|-
 +
! 1
 +
| Execute
 +
|-
 +
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
# kill -s info 40947
+
E.g.
  
The dd process will report its status in the terminal its running in.
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== Transferring a large file via FAT32 file system ==
+
== Updating config files ==
  
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
+
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
  
  $ split -b 4000m input.tgz input.tgz-parts-
+
  $ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
Then copy the small files and reassemble:
+
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
  
$ cat input.tgz-parts-* > output.tgz
+
The merge program is a part of the RCS package. If you don't have it:
  
= NFS =
+
$ sudo apt-get install rcs
  
== List NFS shares ==
+
== Listing open files ==
  
To e.g. show NFS shares on 'love':
+
Use lsof to list open files. E.g.:
  
  $ showmount -e love
+
  # lsof
  
= Compression =
+
See man lsof for options.
  
== How to use pigz with tar ==
+
== List permissions on a whole directory path ==
  
See [https://stackoverflow.com/a/39904353 here]:
+
E.g.:
  
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
  $ namei -om /home/jj5/workspace
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
Outputs:
  
== Best compression with tar ==
+
f: /home/jj5/workspace/
 
+
  drwxr-xr-x root root /
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
+
  drwxr-xr-x root root home
 +
  drwxr-xr-x jj5  jj5  jj5
 +
  drwxr-xr-x jj5  jj5  workspace
 +
 
 +
== Counting non-blank lines in a file ==
 +
 
 +
E.g.:
 +
 
 +
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
export GZIP=-9
+
== Cloning one directory to another with rsync ==
tar cvzf file.tar.gz /path/to/directory
 
  
or
+
E.g.:
  
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
+
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
  
== Best parallel compression with pigz ==
+
== Counting number of files in current directory and all subdirectories ==
  
  $ pigz --best
+
  $ ls -AlhR . | egrep '^-' | wc -l
  
== Best parallel compression with xz ==
+
== Counting number of directories in current directory and all subdirectories ==
  
  $ xz -9e -T 0
+
  $ ls -AlhR . | egrep '^d' | wc -l
  
== Reporting compression ratios with xz ==
+
== Getting the status of a 'dd' process ==
  
e.g.
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
root@love:/data/image/archive# xz -l *
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
 
    1      3    372.2 MiB    442.3 MiB  0.841  CRC64  1999.txz
 
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64  2001.txz
 
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64  2002.txz
 
    1      9    568.5 MiB  1,660.2 MiB  0.342  CRC64  2003.txz
 
    1    639    66.8 GiB    119.6 GiB  0.558  CRC64  2004.txz
 
    1    313    12.7 GiB    58.6 GiB  0.217  CRC64  2005.txz
 
    1    414    35.0 GiB    77.4 GiB  0.452  CRC64  2006.txz
 
    1    485    44.5 GiB    90.9 GiB  0.490  CRC64  2007.txz
 
    1  1,690    150.0 GiB    316.8 GiB  0.473  CRC64  2008.txz
 
    1      3    457.9 MiB    526.0 MiB  0.871  CRC64  2009.txz
 
    1    168    27.3 GiB    31.4 GiB  0.868  CRC64  2010.txz
 
    1      4    477.1 MiB    702.8 MiB  0.679  CRC64  2011.txz
 
-------------------------------------------------------------------------------
 
    12  3,768    344.6 GiB    705.5 GiB  0.488  CRC64  12 files
 
  
= Symbolic-link management =
+
# kill -s info 40947
  
== Data used by sym-linked files:
+
The dd process will report its status in the terminal its running in.
  
This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:
+
== Transferring a large file via FAT32 file system ==
  
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
  
= File searching =
+
$ split -b 4000m input.tgz input.tgz-parts-
  
== Finding a file with a particular name ==
+
Then copy the small files and reassemble:
  
  $ find -iname "*some-part-of-the-file-name*"
+
  $ cat input.tgz-parts-* > output.tgz
  
Will start searching from the current directory, so maybe
+
== Find the difference between two directories ==
  
  $ cd /
+
  $ diif -qr $DIR_A $DIR_B
  
first. For a case-sensitive search:
+
== Merging two directories ==
  
  $ find -name "*eXaCT CaSE*"
+
  $ cp -RT source/ destination/
  
== Finding a file with particular content ==
+
Files from source will be merged into destination.
  
To search in /etc/ for a file with particular content:
+
== Generating a replacement file ==
  
$ grep -R "search-string" /etc/*
+
So you generate the file into a temp file, then hard link the temp file to where you want the replacement to go, then you delete the temp file:
  
To search the current directory for *.cs files containing the word "Up":
+
$ generate-file.sh > file.txt.tmp
 +
$ ln -f file.txt.tmp file.txt
 +
$ rm file.txt.tmp
  
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
= NFS =
  
== Finding a list of files with particular content ==
+
== List NFS shares ==
  
E.g. to find all the files with the word 'creativity':
+
To e.g. show NFS shares on 'love':
  
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
  $ showmount -e love
  
== Using the locate command to find files ==
+
= Compression =
  
$ locate part-of-filename
+
== How to use pigz with tar ==
  
E.g.
+
See [https://stackoverflow.com/a/39904353 here]:
  
  $ locate texvc
+
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
== Updating locate command's database ==
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
# updatedb
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
== Select a random line from a text file ==
+
Fast pack:
  
  $ shuf -n 1 input.txt
+
  tar -I 'pigz --fast' -cf my.tar.gz whatver
  
== Extra context for grep ==
+
Best pack:
  
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
$ grep -B 3 -A 1 ...
+
Fast unpack:
  
= Job control =
+
tar -I pigz -xf my.tar.gz
  
== Stopping a running process ==
+
== Best compression with tar ==
  
Press Ctrl+Z to stop a running process.
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
== Listing current jobs and their status ==
+
export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
$ jobs
+
or
  
== Resuming a stopped job in the backgroud ==
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
To resume a stopped process in the background
+
== Best parallel compression with pigz ==
  
  $ bg %1
+
  $ pigz --best
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Best parallel compression with xz ==
  
== Resuming a stopped job in the foreground ==
+
$ xz -9e -T 0
  
To resume a stopped process in the foreground
+
== Reporting compression ratios with xz ==
  
$ fg %1
+
e.g.
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
root@love:/data/image/archive# xz -l *
 +
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
 +
    1       3    372.2 MiB    442.3 MiB  0.841  CRC64  1999.txz
 +
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64  2001.txz
 +
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64  2002.txz
 +
    1      9    568.5 MiB  1,660.2 MiB  0.342  CRC64  2003.txz
 +
    1    639    66.8 GiB    119.6 GiB  0.558  CRC64  2004.txz
 +
    1    313    12.7 GiB    58.6 GiB  0.217  CRC64  2005.txz
 +
    1    414    35.0 GiB    77.4 GiB  0.452  CRC64  2006.txz
 +
    1    485    44.5 GiB    90.9 GiB  0.490  CRC64  2007.txz
 +
    1  1,690    150.0 GiB    316.8 GiB  0.473  CRC64  2008.txz
 +
    1      3    457.9 MiB    526.0 MiB  0.871  CRC64  2009.txz
 +
    1    168    27.3 GiB    31.4 GiB  0.868  CRC64  2010.txz
 +
    1      4    477.1 MiB    702.8 MiB  0.679  CRC64  2011.txz
 +
-------------------------------------------------------------------------------
 +
    12  3,768    344.6 GiB    705.5 GiB  0.488  CRC64  12 files
  
== Killing a stopped job ==
+
= Symbolic-link management =
  
To kill a job
+
== Data used by sym-linked files:
  
$ kill %1
+
This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
== Periodically run a program and watch its output ==
+
= File searching =
  
$ watch /your/command
+
== Finding a file with a particular name ==
  
= Debian/Ubuntu package management =
+
$ find -iname "*some-part-of-the-file-name*"
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
Will start searching from the current directory, so maybe
  
== configuring debconf ==
+
$ cd /
  
# dpkg-reconfigure debconf
+
first. For a case-sensitive search:
  
Set priority to low to get asked detailed questions.
+
$ find -name "*eXaCT CaSE*"
  
== Showing list of installed packages ==
+
== Finding a file with particular content ==
  
# dpkg --get-selections
+
To search in /etc/ for a file with particular content:
  
== Searching for installed package ==
+
$ grep -R "search-string" /etc/*
  
# dpkg --get-selections | grep package-name
+
To search the current directory for *.cs files containing the word "Up":
  
or
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
# aptitude search package-name
+
== Finding a list of files with particular content ==
  
== Showing which files are installed as part of a package ==
+
E.g. to find all the files with the word 'creativity':
  
  # dpkg -L package-name
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
== Installing a package ==
+
== Using the locate command to find files ==
  
  # apt-get install package-name
+
  $ locate part-of-filename
  
== Uninstalling a package ==
+
E.g.
  
  # apt-get remove package-name
+
  $ locate texvc
  
== Showing system architecture ==
+
== Updating locate command's database ==
  
  $ dpkg --print-architecture
+
  # updatedb
  
== Showing which package a file belongs to ==
+
== Select a random line from a text file ==
  
  $ which echo
+
  $ shuf -n 1 input.txt
/bin/echo
 
$ dpkg -S /bin/echo
 
coreutils: /bin/echo
 
$ dpkg -l | grep coreutils
 
ii  coreutils                        6.10-6                  The GNU core utilities
 
  
== Showing package information ==
+
== Extra context for grep ==
  
$ apt-cache showpkg coreutils
+
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
  
Or for even more information:
+
$ grep -B 3 -A 1 ...
  
$ apt-cache show coreutils
+
= Job control =
  
== List all installed packages with package version info ==
+
== Stopping a running process ==
  
dpkg-query -l
+
Press Ctrl+Z to stop a running process.
  
== Reporting which version of a package is installed ==
+
== Listing current jobs and their status ==
  
  $ dpkg -l | grep package-name
+
  $ jobs
  
E.g.:
+
== Resuming a stopped job in the backgroud ==
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
To resume a stopped process in the background
ii  augeas-lenses                  0.7.0-1ubuntu1                Set of lenses needed by libaugeas0 to parse
 
ii  libaugeas0                      0.7.0-1ubuntu1                The augeas configuration editing library and
 
  
== Comprehensive upgrade ==
+
$ bg %1
  
Try the following:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
# apt-get update
+
== Resuming a stopped job in the foreground ==
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
To resume a stopped process in the foreground
  
  $ apt-cache search . | sort -d | less
+
  $ fg %1
  
= Networking =
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== net-tools vs iproute2 ==
+
== Killing a stopped job ==
  
The older 'net-tools' package has been replaced with 'iproute2' e.g. in [https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#iproute2 stretch].
+
To kill a job
  
{|class="wikitable"
+
  $ kill %1
! legacy net-tools commands
 
! iproute2 replacement commands
 
|-
 
| arp      || ip n (ip neighbor)
 
|-
 
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 
|-
 
| iptunnel || ip tunnel
 
|-
 
| iwconfig || iw
 
|-
 
| nameif  || ip link, ifrename
 
|-
 
| netstat || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 
|-
 
| route    || ip r (ip route)
 
|}
 
  
== Restart networking ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
For servers:
+
== Periodically run a program and watch its output ==
  
  # service networking restart
+
  $ watch /your/command
  
For desktops:
+
= Debian/Ubuntu package management =
  
# service network-manager restart
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
== Pinging with particular packet size ==
+
== configuring debconf ==
  
  $ ping -M do -s <packet size in bytes> <host>
+
  # dpkg-reconfigure debconf
 +
 
 +
Set priority to low to get asked detailed questions.
  
E.g.
+
== Showing list of installed packages ==
  
  $ ping -M do -s 1400 charity.progclub.org
+
  # dpkg --get-selections
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Searching for installed package ==
  
  # ip route add <host> dev <interface> advmss <packet size>
+
  # dpkg --get-selections | grep package-name
  
E.g.
+
or
  
  # ip route add 10.0.0.1 dev eth0 advmss 1400
+
  # aptitude search package-name
  
== Dropping configured MMS for a particular IP address ==
+
== Showing which files are installed as part of a package ==
  
  # ip route flush <host>
+
  # dpkg -L package-name
  
E.g.
+
== Installing a package ==
  
  # ip route flush 10.0.0.1
+
  # apt-get install package-name
  
== Listing open ports and socket information ==
+
== Uninstalling a package ==
  
Including which process is listening on which port.
+
# apt-get remove package-name
  
# netstat -tulpn
+
== Showing system architecture ==
  
Or use the 'ss' command:
+
$ dpkg --print-architecture
  
# ss -s
+
== Showing which package a file belongs to ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
$ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
# lsof -Pnl +M -i4
+
== Showing package information ==
  
You might need to install the lsof package:
+
$ apt-cache showpkg coreutils
  
# apt-get install lsof
+
Or for even more information:
  
== Query for DNS MX record ==
+
$ apt-cache show coreutils
  
$ nslookup
+
== List all installed packages with package version info ==
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
dpkg-query -l
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
== Reporting which version of a package is installed ==
  
== Using nmap to list open ports on remote host ==
+
$ dpkg -l | grep package-name
  
To check the 1,000 most common ports:
+
E.g.:
  
  # nmap server.example.com
+
  root@hope:~/letsencrypt# dpkg -l | grep augeas
 +
ii  augeas-lenses                  0.7.0-1ubuntu1                Set of lenses needed by libaugeas0 to parse
 +
ii  libaugeas0                      0.7.0-1ubuntu1                The augeas configuration editing library and
  
Or for a specific port range (e.g. 101 to 102):
+
== Comprehensive upgrade ==
  
# nmap -p 101-102 server.example.com
+
Try the following:
  
Or for all ports (1 to 65,535):
+
# apt-get update
 +
# apt-get dist-upgrade
 +
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
# nmap -p- server.example.com
+
== Searching all available packages ==
  
== Network monitoring ==
+
$ apt-cache search . | sort -d | less
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
== Reporting unattended upgrades status ==
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
You can watch network traffic in real-time with nload:
+
== Searching for Debian packages and versions ==
  
# nload -u M
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
== Reporting network (NIC) speed ==
+
= Networking =
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
== Determining throughput between two hosts ==
  
  # dmesg | grep eth0
+
  # apt install iperf3
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
On the server:
  
== Path MTU discovery ==
+
# iperf3 -s
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
On the client:
  
  # tracepath host.example.com
+
  # iperf3 -c $SERVER_IP
  
== Listing available Ethernet devices ==
+
For more info see: [https://www.cyberciti.biz/faq/how-to-test-the-network-speedthroughput-between-two-linux-servers/ How to test the network speed/throughput between two Linux servers].
  
To see a list of NICs available on the host:
+
== net-tools vs iproute2 ==
  
$ cat /proc/net/dev
+
The older 'net-tools' package has been replaced with 'iproute2' e.g. in [https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#iproute2 stretch].
  
Also
+
{|class="wikitable"
 +
! legacy net-tools commands
 +
! iproute2 replacement commands
 +
|-
 +
| arp      || ip n (ip neighbor)
 +
|-
 +
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 +
|-
 +
| iptunnel || ip tunnel
 +
|-
 +
| iwconfig || iw
 +
|-
 +
| nameif  || ip link, ifrename
 +
|-
 +
| netstat  || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 +
|-
 +
| route    || ip r (ip route)
 +
|}
  
$ ip link
+
== Restart networking ==
  
== 59 Linux Networking commands and scripts ==
+
For servers:
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
# service networking restart
  
== Links ==
+
For desktops:
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
# service network-manager restart
  
= IPTables =
+
== Pinging with particular packet size ==
  
== Applying firewall rules ==
+
$ ping -M do -s <packet size in bytes> <host>
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
E.g.
  
  $ sudo vim /etc/iptables.test.rules
+
  $ ping -M do -s 1400 charity.progclub.org
$ sudo /sbin/iptables -F
 
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 
$ sudo iptables -L
 
$ sudo -s
 
# iptables-save > /etc/iptables.up.rules
 
# exit
 
  
= ufw =
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
== Denying hosts with ufw ==
+
# ip route add <host> dev <interface> advmss <packet size>
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
E.g.
  
= Bind9 =
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
== Viewing Bind9 querylog ==
+
== Dropping configured MMS for a particular IP address ==
  
  $ sudo rndc querylog
+
  # ip route flush <host>
$ tail -f /var/log/syslog
 
  
= IPSec =
+
E.g.
  
== Disabling IPSec ==
+
# ip route flush 10.0.0.1
  
# setkey -FP
+
== Listing open ports and socket information ==
  
= OpenSSL =
+
Including which process is listening on which port.
  
== Debugging IMAPS with OpenSSL ==
+
# netstat -tulpn
  
# openssl s_client -connect localhost:993
+
Or use the 'ss' command:
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
$ openssl s_client -connect www.example.com:443
+
== Listing open IPv4 connections ==
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
# lsof -Pnl +M -i4
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
You might need to install the lsof package:
  
= Pluggable Authentication Modules (PAM) =
+
# apt-get install lsof
  
== Links ==
+
== Query for DNS MX record ==
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
= SSH =
+
== Query for DNS SOA record ==
  
== Configuring SSH key login ==
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
== Using nmap to list open ports on remote host ==
  
$ ssh-keygen -t rsa
+
To check the 1,000 most common ports:
  
Copy the public key from the client to the server:
+
# nmap server.example.com
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
Or for a specific port range (e.g. 101 to 102):
  
Configure the authorized keys on the server:
+
# nmap -p 101-102 server.example.com
  
$ ssh user@example.org
+
Or for all ports (1 to 65,535):
$ mkdir ~/.ssh
 
$ chmod go-w .ssh
 
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 
$ chmod 600 ~/.ssh/authorized_keys
 
$ rm ~/id_rsa.pub
 
  
== Tunneling over SSH ==
+
# nmap -p- server.example.com
  
For example, connecting a remote MySQL server to the localhost:
+
== Network monitoring ==
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
 +
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 +
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 +
# Bandwidth per process: nethogs
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
== nload ==
 +
 
 +
You can watch network traffic in real-time with nload:
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
# nload -u M
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
== Reporting network (NIC) speed ==
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
* run putty.exe
+
# dmesg | grep eth0
* Connection -> SSH -> Tunnels
+
# mii-tool -v eth0
** Port forwarding: source port to 3306
+
# ethtool eth0
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
Note: use ifconfig to get device name.
  
To see what's going on with your ssh connections,
+
== Path MTU discovery ==
  
$ ssh -v user@host
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
Or
+
# tracepath host.example.com
  
$ ssh -vv user@host
+
== Listing available Ethernet devices ==
  
== Unlocking SSH key for session ==
+
To see a list of NICs available on the host:
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  $ cat /proc/net/dev
[Desktop Entry]
 
Type=Application
 
Name=ssh-add
 
Comment=Adds my private key to my session.
 
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Links ==
+
Also
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
$ ip link
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
== 59 Linux Networking commands and scripts ==
  
== cat EOF ==
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
$ cat > output <<EOF
+
== Links ==
> text
 
> EOF
 
  
$ cat output
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
text
 
  
= Script =
+
= IPTables =
  
== Creating a session log with script ==
+
== Applying firewall rules ==
  
$ script -t 2> timing
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
$ sudo vim /etc/iptables.test.rules
 
+
$ sudo /sbin/iptables -F
== Replaying a scripted session ==
+
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 +
$ sudo iptables -L
 +
$ sudo -s
 +
# iptables-save > /etc/iptables.up.rules
 +
# exit
  
$ scriptreplay timing
+
== Blocking an IP address with iptables ==
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
To drop IP address 1.2.3.4:
  
= Screen =
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
== Creating a new screen or reconnecting to a detached screen ==
+
= ufw =
  
$ screen -R
+
== Denying hosts with ufw ==
  
== Detaching a screen ==
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
$ screen -D
+
= Bind9 =
  
== Reconnecting to screen ==
+
== Viewing Bind9 querylog ==
  
  $ screen -D
+
  $ sudo rndc querylog
  $ screen -R
+
  $ tail -f /var/log/syslog
  
I have a script in ~/bin/reconnect like so,
+
= IPSec =
  
#!/bin/bash
+
== Disabling IPSec ==
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
# setkey -FP
  
== Scrolling in screen ==
+
= OpenSSL =
  
See [https://www.saltycrane.com/blog/2008/01/how-to-scroll-in-gnu-screen/ How to scroll in GNU Screen]. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.
+
== Debugging IMAPS with OpenSSL ==
  
= tmux =
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
== Live collaboration with tmux ==
+
== Debugging HTTPS with OpenSSL ==
  
User A:
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
tmux -S /tmp/collab
+
== Links ==
chmod 777 /tmp/collab
 
  
User B:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
tmux -S /tmp/collab attach
+
= Pluggable Authentication Modules (PAM) =
  
= Vim =
+
== Links ==
  
== First, why Vim? ==
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
= SSH =
  
== Visual modes ==
+
== Configuring SSH key login ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
== Configuring spaces instead of tabs ==
+
$ ssh-keygen -t rsa
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
Copy the public key from the client to the server:
  
  $ vim ~/.vimrc
+
  $ scp ~/.ssh/id_rsa.pub user@example.org:
  
and include the following lines:
+
Configure the authorized keys on the server:
  
  set tabstop=2
+
  $ ssh user@example.org
  set shiftwidth=2
+
  $ mkdir ~/.ssh
  set expandtab
+
  $ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
== Configuring syntax highlighting ==
+
== Tunneling over SSH ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
For example, connecting a remote MySQL server to the localhost:
  
Use:
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
:syntax on
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
to turn on syntax highlighting.
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
Use:
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
:syntax off
+
== Tunneling over SSH with PuTTY ==
  
to turn off syntax highlighting.
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
To always use syntax highlighting:
+
* run putty.exe
 
+
* Connection -> SSH -> Tunnels
$ vim ~/.vimrc
+
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
and add:
+
== Enabling verbose SSH logging ==
  
syntax on
+
To see what's going on with your ssh connections,
  
To get a list of supported colour schemes open vim and type:
+
$ ssh -v user@host
  
:colorscheme[space][Ctrl+D]
+
Or
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
$ ssh -vv user@host
  
colorscheme desert
+
== Unlocking SSH key for session ==
  
== Inserting a TAB character when expandtab is on ==
+
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
  
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
+
== Links ==
  
Press Ctrl+V TAB to insert a literal tab character.
+
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
 +
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
  
Or you can disable tab expansion altogether with:
+
= Standard IO =
  
:set expandtab!
+
== cat EOF ==
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  :%s/^\s*/&&/g
+
  $ cat output
 +
text
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
= Script =
  
== Recording and replaying a macro ==
+
== Creating a session log with script ==
  
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
+
$ script -t 2> timing
  
== Deleting to end of line ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
d$
+
== Replaying a scripted session ==
  
== Deleting to beginning of line ==
+
$ scriptreplay timing
  
d^
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
== Finding text ==
+
= Screen =
  
To search forward for "text":
+
== Creating a new screen or reconnecting to a detached screen ==
  
  /text
+
  $ screen -R
  
To search backward for "text":
+
== Detaching a screen ==
  
  ?text
+
  $ screen -D
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
== Reconnecting to screen ==
  
== Finding and replacing text ==
+
$ screen -D
 +
$ screen -R
  
To replace the first instance of "search" on the current line with "destroy":
+
I have a script in ~/bin/reconnect like so,
  
  :s/search/destroy/
+
  #!/bin/bash
 +
screen -D
 +
screen -R
  
To replace all instances of "search" on the current line with "destroy":
+
This will detach your last screen, and reconnect it on the current terminal.
  
:s/search/destroy/g
+
== Scrolling in screen ==
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
See [https://www.saltycrane.com/blog/2008/01/how-to-scroll-in-gnu-screen/ How to scroll in GNU Screen]. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.
  
:13,37 s/search/destroy/g
+
= tmux =
  
To replace all instances of "search" in the entire file with "destroy":
+
== Live collaboration with tmux ==
  
:%s/search/destroy/g
+
User A:
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
To set the line-ending to Unix line endings run the command:
+
User B:
  
  :setlocal ff=unix
+
  tmux -S /tmp/collab attach
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
= Vim =
  
== Disabling auto-indent etc. to paste from clipboard ==
+
== First, why Vim? ==
  
To disable smart indenting when you're going to paste in text:
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
:set paste
+
== Visual modes ==
  
To turn it off again:
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
:set nopaste
+
== Configuring spaces instead of tabs ==
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
== Positioning windows ==
+
$ vim ~/.vimrc
  
Use -o for horizontal split, e.g.:
+
and include the following lines:
  
  vim -o a.txt b.txt
+
  set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
Use -O for vertical split, e.g.:
+
== Configuring syntax highlighting ==
  
vim -o a.txt b.txt
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
Use:
  
Use ^W and &lt; or &gt; to resize windows.
+
:syntax on
  
== To indent a block of text in Vim ==
+
to turn on syntax highlighting.
  
Use the > command. E.g. to indent five lines:
+
Use:
  
  5 > >
+
  :syntax off
  
Press . (dot) to keep indenting.
+
to turn off syntax highlighting.
  
Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:
+
To always use syntax highlighting:
  
  > %
+
  $ vim ~/.vimrc
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
and add:
  
== Open a file in a new window/tab ==
+
syntax on
  
To open a file on the left hand side:
+
To get a list of supported colour schemes open vim and type:
  
  :vert new filename.ext
+
  :colorscheme[space][Ctrl+D]
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
To open a file at the top:
+
colorscheme desert
  
:new filename.ext
+
== Inserting a TAB character when expandtab is on ==
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
  
== Explore files in Vim ==
+
Press Ctrl+V TAB to insert a literal tab character.
  
Enter:
+
Or you can disable tab expansion altogether with:
  
  :Explore
+
  :set expandtab!
  
== Switch between Vim tabs ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
Use gt and gT.
+
:%s/^\s*/&&/g
  
== Switch between Vim windows ==
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
To toggle between open windows use:
+
== Recording and replaying a macro ==
  
Ctrl+W W
+
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
 +
 
 +
== Deleting to end of line ==
  
To move in a direction use:
+
d$
  
Ctrl+W h/j/k/l
+
== Deleting to beginning of line ==
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
d^
  
== Insert block comment in Vim ==
+
== Finding text ==
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
To search forward for "text":
  
So it's:
+
/text
  
# Ctrl+V (Note: not Shift+V!)
+
To search backward for "text":
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
?text
  
To navigate to the matching beginning or end tag use '%'.
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
== Finding and replacing text ==
  
== Auto-format HTML tags ==
+
To replace the first instance of "search" on the current line with "destroy":
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
:s/search/destroy/
  
# first join all the lines - ggVGgJ
+
To replace all instances of "search" on the current line with "destroy":
# Now break tags to new lines - :%s/>\s*</>\r</g
 
# Now set filetype - :set ft=html (you can do this before too)
 
# Now Indent - ggVG=
 
  
== Links ==
+
:s/search/destroy/g
  
* [http://www.vim.org/ Vim: the editor]
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 
* [http://vim.wikia.com/wiki/File_format File format]
 
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
 
  
== Create PDF from text using Vim ==
+
:13,37 s/search/destroy/g
  
Generate PDF from input.txt with:
+
To replace all instances of "search" in the entire file with "destroy":
  
  $ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
+
  :%s/search/destroy/g
  
Examine output with:
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
$ okular doc.pdf
+
To set the line-ending to Unix line endings run the command:
  
= Write =
+
:setlocal ff=unix
  
== Talking to other users on the system ==
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
== Disabling auto-indent etc. to paste from clipboard ==
  
1. SSH to <username>@<hostname> and login with your username and password.
+
To disable smart indenting when you're going to paste in text:
  
2. Issue the following command to find out who is logged onto the system:
+
:set paste
  
$ who
+
To turn it off again:
  
3. Issue the following command to talk to a specific user:
+
:set nopaste
  
$ write <username>
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
== Positioning windows ==
  
= Date =
+
Use -o for horizontal split, e.g.:
  
== Reporting the time on the server ==
+
vim -o a.txt b.txt
  
$ date
+
Use -O for vertical split, e.g.:
  
== Reporting UTC time ==
+
vim -o a.txt b.txt
  
$ date --utc
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
Use ^W and &lt; or &gt; to resize windows.
  
$ date="`date +%F-%H%M%S`"
+
== To indent a block of text in Vim ==
  
== Getting the year in four digits ==
+
Use the > command. E.g. to indent five lines:
  
  $ year="`date +%Y`"
+
  5 > >
  
== Getting the month in two digits ==
+
Press . (dot) to keep indenting.
  
$ month="`date +%m`"
+
Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:
  
== Getting the day of the month in two digits ==
+
> %
  
$ day="`date +%d`"
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
== Getting yesterday's date ==
+
== Open a file in a new window/tab ==
  
$ date --date='1 day ago' +%Y-%m-%d
+
To open a file on the left hand side:
  
== Converting Unix time (seconds since epoch) ==
+
:vert new filename.ext
  
For timestamp '1501370200':
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
$ date -d @1501370200 +%F-%H%M%S
+
To open a file at the top:
  
== Running timedatectl from systemd ==
+
:new filename.ext
  
There's a new command bundled with systmed:
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
# timedatectl
+
== Explore files in Vim ==
  
It reports on (and controls) how the system time is configured.
+
Enter:
  
= MySQL =
+
:Explore
  
== Run mysql without authentication/authorisation ==
+
== Switch between Vim tabs ==
  
# service mysql stop
+
Use gt and gT.
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
== Switch between Vim windows ==
  
# mysql -u root mysql
+
To toggle between open windows use:
  
To stop the unauthenticated service:
+
Ctrl+W W
  
# mysqladmin shutdown
+
To move in a direction use:
  
Then restart a normal service:
+
Ctrl+W h/j/k/l
  
# service mysql start
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
== Logging all database queries ==
+
== Insert block comment in Vim ==
  
# vim /etc/mysql/my.cnf
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
In the [mysqld] section add:
+
So it's:
  
log=/tmp/mysql.log
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
Then:
+
== Navigate to matching tag ==
  
# service mysql restart
+
To navigate to the matching beginning or end tag use '%'.
  
Watch the log with:
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
# tail -f /tmp/mysql.log
+
== Auto-format HTML tags ==
  
== Dumping a MySQL database ==
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
You can dump the database into a file using:  
+
# first join all the lines - ggVGgJ
+
# Now break tags to new lines - :%s/>\s*</>\r</g
$ mysqldump -h hostname -u user --password=password databasename > filename
+
# Now set filetype - :set ft=html (you can do this before too)
 +
# Now Indent - ggVG=
  
== Loading a MySQL database from a dump file ==
+
== Links ==
  
You can create a database using:
+
* [http://www.vim.org/ Vim: the editor]
 +
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 +
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 +
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 +
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 +
* [http://vim.wikia.com/wiki/File_format File format]
 +
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 +
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
  
$ echo create database databasename | mysql -h hostname -u user -p
+
== Create PDF from text using Vim ==
  
You can restore a database using:
+
Generate PDF from input.txt with:
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
# mysql -h localhost -u root --password=<password>
+
Examine output with:
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
$ okular doc.pdf
  
# mysql -h localhost -u root --password=<password>
+
= Write =
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
== Talking to other users on the system ==
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
1. SSH to <username>@<hostname> and login with your username and password.
  
Check the SSL version in use:
+
2. Issue the following command to find out who is logged onto the system:
  
  show status like 'Ssl_version';
+
  $ who
  
Or check the cipher in use:
+
3. Issue the following command to talk to a specific user:
  
  show status like 'Ssl_cipher';
+
  $ write <username>
  
= Apache =
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
== Reporting loaded Apache modules ==
+
= Date =
  
# apache2ctl -M
+
== Reporting the time on the server ==
  
== Maintaining .htaccess passwords ==
+
$ date
  
To add or modify the password for a user:
+
== Reporting UTC time ==
  
  $ htpasswd /etc/apache2/passwd username
+
  $ date --utc
  
== Configuring PHP session timeout in .htaccess ==
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
For a session timeout of 9 hours:
+
$ date="`date +%F-%H%M%S`"
  
php_value session.cookie_lifetime 32400
+
== Getting the year in four digits ==
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
$ year="`date +%Y`"
  
php_flag magic_quotes_gpc Off
+
== Getting the month in two digits ==
  
== Requiring HTTP Auth in .htaccess ==
+
$ month="`date +%m`"
  
AuthType Basic
+
== Getting the day of the month in two digits ==
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
$ day="`date +%d`"
  
The hard way
+
== Getting yesterday's date ==
  
  $ sudo /etc/init.d/apache2 restart
+
  $ date --date='1 day ago' +%Y-%m-%d
  
The graceful way (avoids dropping active connections)
+
== Converting Unix time (seconds since epoch) ==
  
$ sudo apache2ctl graceful
+
For timestamp '1501370200':
  
== Allowing directory browsing ==
+
$ date -d @1501370200 +%F-%H%M%S
  
To show directory index pages, in the apache config file:
+
== Running timedatectl from systemd ==
  
<Directory /var/www/data>
+
There's a new command bundled with systmed:
  Options Indexes
 
</Directory>
 
  
= C =
+
# timedatectl
  
== Locating memset function ==
+
It reports on (and controls) how the system time is configured.
  
The memset function is in &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
+
= MySQL (and MariaDB) =
  
== Links ==
+
== Run mysql without authentication/authorisation ==
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
# service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
= PHP =
+
Then you can connect without a password, e.g.:
  
== Including a file relative to the including file ==
+
# mysql -u root mysql
  
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
To stop the unauthenticated service:
  
== Enabling error reporting ==
+
# mysqladmin shutdown
  
error_reporting( E_ALL | E_STRICT );
+
Then restart a normal service:
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
# service mysql start
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
== Logging all database queries ==
  
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
  # vim /etc/mysql/my.cnf
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
In the [mysqld] section add:
  
  ini_set( 'html_errors', 'off' );
+
  log=/tmp/mysql.log
  
== Report PHP modules ==
+
Then:
  
  $ php -m
+
  # service mysql restart
  
== PHP Security Best Practices For Sys Admins ==
+
Watch the log with:
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
# tail -f /tmp/mysql.log
  
= BASH scripting =
+
Or:
 +
 
 +
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
my_logs.txt will be in /var/lib/mysql
  
== Telling a script to run in bash ==
+
== Dumping a MySQL database ==
  
The first line of the file should be:
+
You can dump the database into a file using:  
 +
 +
$ mysqldump -h hostname -u user --password=password databasename > filename
  
#!/bin/bash
+
== Loading a MySQL database from a dump file ==
  
== Checking if a command-line argument was passed in ==
+
You can create a database using:
  
  if [ -n "$1" ]; then
+
  $ echo create database databasename | mysql -h hostname -u user -p
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
if [ "$1" = "" ]; then
+
== Creating a MySQL user ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
if [ -z "$1" ]; then
+
== Granting all MySQL user permissions ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
cd /my/path
+
== Select domain name from email address ==
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
Check if file exists:
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
if [ -f "/my/file" ]; then
+
Check the SSL version in use:
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
show status like 'Ssl_version';
  
if [ ! -f "/my/file" ]; then
+
Or check the cipher in use:
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
show status like 'Ssl_cipher';
  
Check if directory exists:
+
== Report on server config ==
  
if [ -d "/my/dir" ]; then
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
SHOW VARIABLES
  
if [ ! -d "/my/dir" ]; then
+
and
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
SHOW STATUS
  
To keep only the latest five backups:
+
and
  
  find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f
+
  SHOW PROCESSLIST
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
== Monitor MySQL activity ==
  
Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.
+
$ watch "mysql -t -e 'show processlist'"
  
== Changing into the script's directory ==
+
= Apache =
  
cd "`dirname $0`"
+
== Reporting loaded Apache modules ==
  
== Getting the absolute path of a relative path ==
+
# apache2ctl -M
  
readlink -f ./some/path
+
== Maintaining .htaccess passwords ==
  
== Creating a temp directory ==
+
To add or modify the password for a user:
  
  dir=`mktemp -d` && cd $dir
+
  $ htpasswd /etc/apache2/passwd username
  
== Reading secret input from stdin ==
+
== Configuring PHP session timeout in .htaccess ==
  
You can read a secret, such as a password, like this:
+
For a session timeout of 9 hours:
  
  echo -n "Enter passphrase: "
+
  php_value session.cookie_lifetime 32400
  stty -echo
+
  php_value session.gc_maxlifetime 32400
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Disabling PHP magic quotes in .htaccess ==
  
== String replacements in bash ==
+
php_flag magic_quotes_gpc Off
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
== Requiring HTTP Auth in .htaccess ==
  
  result=${var/find/replace}
+
  AuthType Basic
 +
AuthName "Speak Friend And Enter"
 +
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
  
To replace all occurrences:
+
== Restarting Apache ==
  
result=${var//find/replace}
+
The hard way
  
A practical example, get an ISO date and turn it into a path:
+
$ sudo /etc/init.d/apache2 restart
  
date="$(date +%Y-%m-%d)"
+
The graceful way (avoids dropping active connections)
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
$ sudo apache2ctl graceful
  
cat << EOF > /tmp/yourfilehere
+
== Allowing directory browsing ==
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
To show directory index pages, in the apache config file:
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
case $space in
+
= C =
[1-6]*)
 
  Message="All is quiet."
 
  ;;
 
[7-8]*)
 
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
 
  ;;
 
9[1-8])
 
  Message="Better hurry with that new disk...  One partition is $space % full."
 
  ;;
 
99)
 
  Message="I'm drowning here!  There's a partition at $space %!"
 
  ;;
 
*)
 
  Message="I seem to be running with an nonexistent amount of disk space..."
 
  ;;
 
esac
 
  
== Using dotglob shopt to match dot-files ==
+
== Locating memset function ==
  
To enable dot-file matching in globs, set the dotglob shell option:
+
The memset function is in &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
  
$ shopt -s dotglob
+
== Links ==
  
== Stopping a script from running if it previously exited due to error ==
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
persistentDataDir=/var/lib/something
+
= PHP =
alarm() {
 
  touch $persistentDataDir/alarm
 
}
 
trap alarm ERR
 
[ -f $persistentDataDir/alarm ] && exit 1
 
  
== Make sure only one instance of a script is running at a time ==
+
== Including a file relative to the including file ==
  
  ephemeralDataDir=/var/run/something
+
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
== Enabling error reporting ==
  
See [https://blog.yossarian.net/2020/01/23/Anybody-can-write-good-bash-with-a-little-effort Anybody can write good bash (with a little effort)].
+
error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
== Run a command using arguments that come from an array ==
+
== Setting an error handler ==
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
  #!/bin/bash
+
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
tabs=("first tab" "second tab")
+
   // ...
args=()
+
  }
for t in "${tabs[@]}" ; do
 
   args+=(-t "$t")
 
done
 
  app "${args[@]}"
 
  
== Display a CSV in columnar or tabular format ==
+
== Disable HTML content in var_dump ==
  
  $ column -t -s , data.csv
+
  ini_set( 'html_errors', 'off' );
  
= Sed =
+
== Report PHP modules ==
  
== Find and replace with sed ==
+
$ php -m
  
To update the current file use '-i'. E.g.:
+
== PHP Security Best Practices For Sys Admins ==
  
sed -i 's/search-text/replace-text/' file
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
= Awk =
+
= BASH scripting =
  
== Listing IP addresses in an Apache web log ==
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
== Telling a script to run in bash ==
  
== Printing space-separated field ==
+
The first line of the file should be:
  
  echo 'no no yes no' | awk '{print $3}'
+
  #!/bin/bash
  
== Printing delimited field ==
+
== Checking if a command-line argument was passed in ==
  
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
  if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
= Subversion =
+
== Checking if a command-line argument was not passed in ==
  
== Setting svn:externals from the command-line ==
+
if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
Or:
  
To set an svn:externals from the command-line:
+
if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
== Checking command exit status ==
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
svn propset svn:externals -F svn.externals .
+
== Checking if a file does/doesn't exist ==
  
== Setting svn:ignore from the command line ==
+
Check if file exists:
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
$ svn propset svn:ignore [file|folder] [path]
+
Check if file doesn't exist:
  
Or use a file and apply recursively:
+
if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
== Checking if a directory does/doesn't exist ==
  
= Git =
+
Check if directory exists:
  
== Showing status of working copy ==
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
git status
+
Check if directory doesn't exist:
  
== Showing repo history ==
+
if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
git log
+
== Deleting old backups ==
  
== Showing remote repositories (including 'origin') ==
+
To keep only the latest five backups:
  
  git remote -v
+
  find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f
  
== Handy git aliases ==
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
Save these to your ~/.gitconfig file.
+
Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
== Changing into the script's directory ==
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
cd "`dirname $0`"
  
To show only the files that have changed, rather than the full line-by-line content:
+
== Getting the absolute path of a relative path ==
  
  dif  = !git diff --name-status
+
readlink -f ./some/path
  
== Show git remote URL ==
+
== Creating a temp directory ==
  
  git config --get remote.origin.url
+
  dir=`mktemp -d` && cd $dir
  
= IRC =
+
== Reading secret input from stdin ==
  
== Instructing ChanServ to op an admin ==
+
You can read a secret, such as a password, like this:
 +
 
 +
echo -n "Enter passphrase: "
 +
stty -echo
 +
read passphrase;
 +
stty echo
 +
echo ""
 +
 
 +
After running the above the secret will be in the $passphrase environment variable.
  
/msg ChanServ op #channel user
+
== String replacements in bash ==
  
E.g.
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
  
  /msg ChanServ op #gnurc jj5
+
  result=${var/find/replace}
  
Sub 'op' for 'deop' to remove op privilege.
+
To replace all occurrences:
  
= C++ =
+
result=${var//find/replace}
  
== C++ books ==
+
A practical example, get an ISO date and turn it into a path:
  
=== Books I want ===
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== Sending a HEREDOC to a file ==
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
cat << EOF > /tmp/yourfilehere
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
+
These contents will be written to the file.
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
+
        This line is indented.
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
+
EOF
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
 
  
=== Books I own ===
+
== Bash case/switch statement ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
 
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
 
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
 
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
 
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
 
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
 
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
 
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
 
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
 
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
 
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
 
  
=== Books I'm not reading ===
+
case $space in
 
+
[1-6]*)
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
  Message="All is quiet."
** Note: 3ed is obsolete. Buy 4ed (above).
+
  ;;
 +
[7-8]*)
 +
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
 +
  ;;
 +
9[1-8])
 +
  Message="Better hurry with that new disk...  One partition is $space % full."
 +
  ;;
 +
99)
 +
  Message="I'm drowning here!  There's a partition at $space %!"
 +
  ;;
 +
*)
 +
  Message="I seem to be running with an nonexistent amount of disk space..."
 +
  ;;
 +
esac
 +
 
 +
== Using dotglob shopt to match dot-files ==
  
=== Books I've read ===
+
To enable dot-file matching in globs, set the dotglob shell option:
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
$ shopt -s dotglob
  
== C++ blogs/articles ==
+
== Stopping a script from running if it previously exited due to error ==
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
persistentDataDir=/var/lib/something
* [http://herbsutter.com/ Herb Sutter's personal blog]
+
alarm() {
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
+
  touch $persistentDataDir/alarm
 +
}
 +
trap alarm ERR
 +
[ -f $persistentDataDir/alarm ] && exit 1
  
== C++ performance tips ==
+
== Make sure only one instance of a script is running at a time ==
  
* ++c can be faster than c++.
+
ephemeralDataDir=/var/run/something
* use const for everything that you possibly can.
+
unlock() {
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
+
  rmdir $ephemeralDataDir/lock
* don't use registers.
+
}
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
+
mkdir $ephemeralDataDir/lock || exit 1;
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
+
trap unlock EXIT
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 
  
= systemd =
+
== BASH programming advice ==
  
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
+
See [https://blog.yossarian.net/2020/01/23/Anybody-can-write-good-bash-with-a-little-effort Anybody can write good bash (with a little effort)].
  
== Following a service log ==
+
== Run a command using arguments that come from an array ==
  
e.g. for bind9:
+
See [https://unix.stackexchange.com/a/412647/356289 here]:
  
  # journalctl -f -u bind9
+
  #!/bin/bash
 
+
tabs=("first tab" "second tab")
or for everything:
+
args=()
 +
for t in "${tabs[@]}" ; do
 +
  args+=(-t "$t")
 +
done
 +
app "${args[@]}"
  
# journalctl -f
+
== Display a CSV in columnar or tabular format ==
  
== System status ==
+
$ column -t -s , data.csv
  
To see spawned services hierarchy:
+
== Maximum command line length ==
  
# systemctl status
+
Technically this is an operating system limit, not a BASH limit.
  
Or for a specific service e.g.:
+
$ getconf ARG_MAX    # Get argument limit in bytes/chars
  
# systemctl status networking
+
= Sed =
  
= SaltStack =
+
== Find and replace with sed ==
  
== Running a command on specified minions ==
+
To update the current file use '-i'. E.g.:
  
From the salt master:
+
sed -i 's/search-text/replace-text/' file
  
salt 'host' cmd.run 'update-locale'
+
= Awk =
  
From the salt minion:
+
== Listing IP addresses in an Apache web log ==
  
  salt-call cmd.run 'update-locale'
+
  awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
  
== Running a command on all minions ==
+
== Printing space-separated field ==
  
  salt '*' cmd.run 'update-locale'
+
  echo 'no no yes no' | awk '{print $3}'
  
== Running a specific state file ==
+
== Printing delimited field ==
  
From the salt master:
+
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
  
salt $MINION_ID state.sls $STATE_FILE
+
= Subversion =
 +
 
 +
== Setting svn:externals from the command-line ==
  
From the salt minion:
+
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
  
salt-call state.sls $STATE_FILE
+
To set an svn:externals from the command-line:
  
== Listing active jobs ==
+
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
 +
svn ci -m 'Adding svn:externals for rdfind-php...'
 +
svn up
  
salt-run jobs.active
+
Or to use a file:
  
== Listing available grains ==
+
svn propset svn:externals -F svn.externals .
  
salt 'example' grains.items
+
== Setting svn:ignore from the command line ==
  
== Listing available pillar ==
+
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
  
  salt 'example' pillar.items
+
  $ svn propset svn:ignore [file|folder] [path]
  
== Reporting a grain value ==
+
Or use a file and apply recursively:
  
e.g. for the 'mem_total' grain:
+
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
  
salt '*' grains.item mem_total
+
= Git =
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
== Showing status of working copy ==
  
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
git status
  
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
== Showing repo history ==
  file.managed:
+
 
    - template: jinja
+
git log
    - user: root
+
 
    - group: root
+
== Showing remote repositories (including 'origin') ==
    - mode: 644
 
    - source: salt://file/srv/zabbix/release/source.txt
 
    - require:
 
      - file: /srv/zabbix/release
 
    - default:
 
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 
  
= KDE =
+
git remote -v
  
== Running user login script (X11/XOrg/XWindows) ==
+
== Handy git aliases ==
  
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
+
Save these to your ~/.gitconfig file.
  
[Desktop Entry]
+
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
Type=Application
 
Name=ssh-add
 
Comment=Adds my private key to my session.
 
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Standard KDE shortcut key bindings ==
+
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
  
{|class="wikitable"
+
To show only the files that have changed, rather than the full line-by-line content:
! Name          !! Shortcut !! Command
 
|-
 
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 
|-
 
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 
|-
 
| Konsole        || Meta+T  || konsole
 
|-
 
| Dolphin        || Meta+E  || dolphin
 
|-
 
| Kate          || Ctrl+Shift+F12 || kate
 
|-
 
| KCalc          || Ctrl+Shift+F11 || kcalc
 
|-
 
| Firefox        || Ctrl+Shift+F10 || firefox
 
|}
 
  
= VirtualBox =
+
  dif  = !git diff --name-status
  
== Mounting a VirtualBox VDI file ==
+
== Show git remote URL ==
  
Note: instead of doing this consider booting with a live CD.
+
git config --get remote.origin.url
  
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
= IRC =
  
Install qemu if necessary:
+
== Instructing ChanServ to op an admin ==
  
  # apt install qemu
+
  /msg ChanServ op #channel user
  
Then you'll need to load the network block device module:
+
E.g.
  
  # rmmod nbd
+
  /msg ChanServ op #gnurc jj5
# modprobe nbd max_part=16
 
  
Attach the .vdi image to one of the nbd you just created:
+
Sub 'op' for 'deop' to remove op privilege.
  
# qemu-nbd -c /dev/nbd0 drive.vdi
+
= C++ =
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
== C++ books ==
  
# mount /dev/nbd0p1 /mnt
+
=== Books I want ===
  
Once you are done, unmount everything and disconnect the device:
+
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
  
# qemu-nbd -d /dev/nbd0
+
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
 +
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 +
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 +
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 +
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
  
= Elasticsearch =
+
=== Books I own ===
  
== Report on health of your Elasticsearch cluster ==
+
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
 
+
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
$ curl http://localhost:9200/_cluster/health?pretty
+
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 
+
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
= Zabbix =
+
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
 +
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
 +
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
 +
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
 +
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
 +
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
 +
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
 +
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
 +
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
 +
 
 +
=== Books I'm not reading ===
  
== Zabbix Agent on Mac OS X ==
+
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
 +
 
 +
=== Books I've read ===
 +
 
 +
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
  
Download and install agent.
+
== C++ blogs/articles ==
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
 +
* [http://herbsutter.com/ Herb Sutter's personal blog]
 +
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
  
Unload agent with:
+
== C++ performance tips ==
  
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
* ++c can be faster than c++.
 +
* use const for everything that you possibly can.
 +
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
 +
* don't use registers.
 +
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 +
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 +
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 +
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 +
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 +
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 +
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 +
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 +
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 +
 
 +
= systemd =
 +
 
 +
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
 +
 
 +
== Following a service log ==
 +
 
 +
e.g. for bind9:
 +
 
 +
# journalctl -f -u bind9
 +
 
 +
or for everything:
 +
 
 +
# journalctl -f
 +
 
 +
== System status ==
 +
 
 +
To see spawned services hierarchy:
 +
 
 +
# systemctl status
 +
 
 +
Or for a specific service e.g.:
 +
 
 +
# systemctl status networking
 +
 
 +
= SaltStack =
 +
 
 +
== Running a command on specified minions ==
 +
 
 +
From the salt master:
 +
 
 +
salt 'host' cmd.run 'update-locale'
 +
 
 +
From the salt minion:
 +
 
 +
salt-call cmd.run 'update-locale'
 +
 
 +
== Running a command on all minions ==
 +
 
 +
salt '*' cmd.run 'update-locale'
 +
 
 +
== Running a specific state file ==
 +
 
 +
From the salt master:
 +
 
 +
salt $MINION_ID state.sls $STATE_FILE
 +
 
 +
From the salt minion:
 +
 
 +
salt-call state.sls $STATE_FILE
 +
 
 +
== Listing active jobs ==
 +
 
 +
salt-run jobs.active
 +
 
 +
== Listing available grains ==
 +
 
 +
salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| Send Ctrl+D    || Pause    || xdotool key "ctrl+d"
 +
|-
 +
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 +
|-
 +
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 +
|-
 +
| Konsole        || Meta+T  || konsole
 +
|-
 +
| Dolphin        || Meta+E  || dolphin
 +
|-
 +
| Firefox        || ScrollLock || firefox
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|}
 +
 
 +
== Shutting down KDE/Plasma ==
 +
 
 +
# /etc/init.d/sddm stop
 +
 
 +
= VirtualBox =
 +
 
 +
== Mounting a VirtualBox VDI file ==
 +
 
 +
Note: instead of doing this consider booting with a live CD.
 +
 
 +
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
 +
 
 +
Install qemu if necessary:
 +
 
 +
# apt install qemu
 +
 
 +
Then you'll need to load the network block device module:
 +
 
 +
# rmmod nbd
 +
# modprobe nbd max_part=16
 +
 
 +
Attach the .vdi image to one of the nbd you just created:
 +
 
 +
# qemu-nbd -c /dev/nbd0 drive.vdi
 +
 
 +
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
 +
 
 +
# mount /dev/nbd0p1 /mnt
 +
 
 +
Once you are done, unmount everything and disconnect the device:
 +
 
 +
# qemu-nbd -d /dev/nbd0
 +
 
 +
= Elasticsearch =
 +
 
 +
== Report on health of your Elasticsearch cluster ==
 +
 
 +
$ curl http://localhost:9200/_cluster/health?pretty
 +
 
 +
= Zabbix =
 +
 
 +
== Zabbix Agent on Mac OS X ==
 +
 
 +
Download and install agent.
 +
 
 +
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
 +
 
 +
Unload agent with:
 +
 
 +
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 
 +
Load agent with:
 +
 
 +
# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 
 +
To add a 'pki' group:
 +
 
 +
# dseditgroup -o create pki
 +
 
 +
To monitor syslog on Mac OS X:
 +
 
 +
# tail -f /var/log/system.log
 +
 
 +
== Installing Zabbix Agent from source on Mac OS X ==
 +
 
 +
Download sources from https://www.zabbix.com/download_sources
 +
 
 +
$ brew update
 +
$ brew install openssl
 +
$ brew install pcre
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install
 +
 
 +
= NetBeans =
 +
 
 +
== NetBeans shortcut keys ==
 +
 
 +
{|class="wikitable sortable"
 +
! Keys        !! Action
 +
|-
 +
| Ctrl+W      || Close active window
 +
|-
 +
| Alt+Shift+K  || Open in Terminal
 +
|-
 +
| Ctrl+U U    || Convert selected text to uppercase
 +
|-
 +
| Ctrl+U L    || Convert selected text to lowercase
 +
|}
  
Load agent with:
+
= XML =
  
# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
== How to pretty-print an XML file ==
  
To add a 'pki' group:
+
$ xmllint --format input.xml > output.xml
  
# dseditgroup -o create pki
+
= ApacheBench =
  
To monitor syslog on Mac OS X:
+
== Run a benchmark with ApacheBench ==
 
 
# tail -f /var/log/system.log
 
  
== Installing Zabbix Agent from source on Mac OS X ==
+
$ ab -n 1000 -c 100 https://www.example.com/
 
 
Download sources from https://www.zabbix.com/download_sources
 
 
 
$ brew update
 
$ brew install openssl
 
$ brew install pcre
 
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
 
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install
 
 
 
= NetBeans =
 
 
 
== NetBeans shortcut keys ==
 
 
 
{|class="wikitable sortable"
 
! Keys        !! Action
 
|-
 
| Ctrl+W      || Close active window
 
|-
 
| Alt+Shift+K  || Open in Terminal
 
|-
 
| Ctrl+U U    || Convert selected text to uppercase
 
|-
 
| Ctrl+U L    || Convert selected text to lowercase
 
|}
 

Latest revision as of 04:24, 28 February 2024

Hi there, I'm John. I just wanted a page where I could document various Linux things that I bump into. This is that page. Thank you ProgClub. :)

Note: I have some other disorganised notes on UNIX, which include a few tips for MacOS. I also have some tips for OS X.

Note: the info on this page is probably Ubuntu (and Debian as an outside chance) specific, because I use Ubuntu pretty much everywhere these days.

You might also be interested in John's hacks.

Quick jump to: NetBeans.

References

Command-line

See Shell Commands I Wish I Knew Earlier for some interesting options.

System

Reporting system specifications from the command-line

Try any of these:

# neofetch
# inxi
# hwinfo --short

You may need to install the relevant package.

Determining which Debian/Ubuntu release your are running

$ lsb_release -r

Or for more information:

$ lsb_release

Determining which Linux/Unix you are running

$ uname

Or,

$ uname -mrs

Or,

$ uname -a

Determining which Linux kernel you are running

$ uname -r

Configuring system swappiness

Swappiness is a number between 0 and 100 that regulates how much the system uses the swap file. I like setting this value to 0 to keep my apps as responsive as possible. Create a file /etc/sysctl.d/local.conf and add this line:

vm.swappiness = 0

If you want to set the value for the current session only:

echo 0 > /proc/sys/vm/swappiness

Hardware information

For information about the hardware attached to your system, check out:

# lshw

And for PCI devices:

# lspci

And for DMI info:

# dmidecode

Note that the dmidecode command (above) will give you information about your system's motherboard. For motherboard info look for 'System Information' and/or 'Base Board Information'.

Or the grand daddy of them all:

# hwinfo

There's also inxi, e.g.:

$ inxi -b

System:    Host: tact Kernel: 4.9.0-4-amd64 x86_64 (64 bit) Desktop: KDE Plasma 5.8.6
           Distro: Debian GNU/Linux 9 (stretch)
Machine:   Device: desktop Mobo: ASUSTeK model: STRIX Z270F GAMING v: Rev 1.xx
           UEFI [Legacy]: American Megatrends v: 0906 date: 03/22/2017
CPU:       Quad core Intel Core i7-7700K (-HT-MCP-) speed/max: 799/4600 MHz
Graphics:  Card: Intel Device 5912
           Display Server: X.Org 1.19.2 drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1920x1080@60.00hz, 1920x1080@60.00hz
           GLX Renderer: Mesa DRI Intel Kabylake GT2 GLX Version: 3.0 Mesa 13.0.6
Network:   Card: Intel Ethernet Connection (2) I219-V driver: e1000e
Drives:    HDD Total Size: 13026.6GB (42.0% used)
RAID:      Devices: 1: /dev/md1 2: /dev/md0
Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5

Motherboard info

# dmidecode -t 2

CPU info

# lscpu

or:

# cat /proc/cpuinfo

RAM info

# dmidecode --type memory

PCI info

# lspci -v

Drive info

# cat /proc/partitions

and:

# hdparm -I /dev/sda

and:

# smartctl --info /dev/sda

You can check if a drive is SSD or not with:

# cat /sys/block/sde/queue/rotational
0=SSD
1=HDD

Viewing syslog and other logs with KSystemLog

Run the 'KSystemLog' program under KDE for a handy log viewer GUI.

CPU

Monitoring CPU clock speed

Try something like this:

$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'

Power

Reporting on PowerShield DEFENDER UPS status

Before running `upsc` ensure service is running:

# upsdrvctl start

To see the status of the PowerShield DEFENDER systems on John's LAN:

$ upsc defender

E.g.:

jj5@orac:~$ upsc defender
Init SSL without certificate database
battery.charge: 100
battery.voltage: 27.40
battery.voltage.high: 26.00
battery.voltage.low: 20.80
battery.voltage.nominal: 24.0
device.type: ups
driver.name: blazer_usb
driver.parameter.pollinterval: 2
driver.parameter.port: auto
driver.parameter.synchronous: no
driver.version: 2.7.4
driver.version.internal: 0.12
input.current.nominal: 5.0
input.frequency: 50.1
input.frequency.nominal: 50
input.voltage: 242.6
input.voltage.fault: 242.6
input.voltage.nominal: 240
output.voltage: 242.6
ups.beeper.status: disabled
ups.delay.shutdown: 30
ups.delay.start: 180
ups.load: 14
ups.productid: 5161
ups.status: OL
ups.type: offline / line interactive
ups.vendorid: 0665

Run commands on PowerShield DEFENDER UPS batteries

You can run "instant commands" using the upscmd command.

We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:

diligence:/srv/salt/conf/app/defender-1200.sls

To see "instant commands" supported by the PowerShield DEFENDER:

$ upscmd -l defender

E.g.:

jj5@orac:~$ upscmd -l defender
Instant commands supported on UPS [defender]:

beeper.toggle - Toggle the UPS beeper
load.off - Turn off the load immediately
load.on - Turn on the load immediately
shutdown.return - Turn off the load and return when power is back
shutdown.stayoff - Turn off the load and remain off
shutdown.stop - Stop a shutdown in progress
test.battery.start - Start a battery test
test.battery.start.deep - Start a deep battery test
test.battery.start.quick - Start a quick battery test
test.battery.stop - Stop the battery test

Service management

Report running services

# service --status-all

Environment

Configuring vim as your editor

Sometimes all you need is:

$ export EDITOR=/usr/bin/vim

Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.

Other times you need to run

# update-alternatives --config editor

And then select vim from the list. This is what you do to configure your visudo editor.

Configuring your locale

$ sudo /usr/sbin/locale-gen en_AU.UTF-8
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8

User and group management

Adding a user

To add a new user on a linux system:

# useradd username
# passwd username

To have the home directory created from '/etc/skel' use the 'adduser' script instead:

# adduser username

Adding a user to a group

To add an existing user to an existing group:

# gpasswd -a username group

e.g. to add user 'jj5' to the 'sudo' group:

# gpasswd -a jj5 sudo

Alternatively you can use adduser, passing the username and group:

# adduser username group

e.g. to add user 'sclaughl' to the 'staff' group:

# adduser sclaughl staff

Disabling a user account

You can disable a user account with:

# passwd -l user

Note: that's a lower-case L, not a one.

Enabling a disabled user account

To can re-enable a locked user account with:

# passwd -u user

Finding which user you are logged in as

To determine which user you are running as enter the command:

$ whoami

Finding which groups you are a member of

To find which groups you are a member of:

$ groups

or

$ groups username

Where 'username' is the username of the user you are querying, e.g.:

$ groups jj5

Finding who else is logged in to the system

To see who else is logged in,

$ who

Running a command as a particular user

To run "svn update" as the user www-data:

$ sudo su -c "svn update" www-data

Reporting user and group info for the current user

$ id

Memory management

Checking available memory

To report memory statistics in megabytes:

$ free -m

Check for swap thrashing

Check your virtual memory status with vmstat:

$ vmstat

Report memory type

Report on RAM DIMMs:

# dmidecode --type 17

Report on RAM and CPU cache (including L1, L2, and L3):

# lshw -short -C memory

Or for more detail:

# lshw -C memory

Video/display management

Viewing EDID data for attached monitor

To view EDID data for an attached monitor (requires the edid-decode package):

$ cd /sys/class/drm
$ ls
$ cd card0-HDMI-A-1
$ edid-decode edid

Process management

Using 'top' for dynamic resource usage reporting

To run top:

$ top

See 15 Practical Linux Top Command Examples for some hints on usage.

To see usage for a specific user run e.g.:

$ top -u jj5

To see full command-line press 'c'.

When you're in 'top' you can:

  • press '1' (one) to toggle CPU aggregation
  • press < and > to change the sort column

Changing memory reporting in 'top'

To run top:

$ top

Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)

Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)

Press 'M' to sort by memory utilisation.

Press 'm' to switch between various display modes.

Showing full command-line in 'top'

To see the full command-line for processes run with -c:

$ top -c

Listing all processes currently running which were started in your current shell session

$ ps -fl

Killing specific processes

# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9

Run a command for a specified time using timeout

$ timeout 3 ping jj5.net

Disk management

Power-off a hard drive

For instance if it's a USB drive or in a mobile rack and you want to remove it.

# udisksctl power-off -b /dev/sdi

Reporting ext4 file-systems mounted without noatime

$ cat /proc/mounts | grep ext | grep -v noatime | sort

Creating a partition table

# parted /dev/xvdf
mktable msdos

Creating a partition

# parted /dev/xvdf
u MiB
mkpart primary 1 100%

Creating an ext4 file-system

# mkfs.ext4 /dev/xvdf1

Listing disk drives

# fdisk -l

(That's an L for "list")

Checking available disk space

$ df -h

Getting disk information

# lsblk

And

# cat /proc/partitions

Or the Grand Daddy of them all:

# lshw -class disk

(Requires the lshw package.)

Getting partition UUID and file-system type

# blkid

Checking for SSD vs magnetic disk

# cat /sys/block/sda/queue/rotational

Will be 0 for SSD and 1 for magnetic.

Monitoring a ZFS server

So some commands I run to keep an eye on my new ZFS servers:

# top
# iotop
# nethogs
# watch free -h
# watch slabtop -o
# slabtop
# watch cat /proc/meminfo
# perf top
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
# watch zpool iostat -v
# zpool iostat -v 2
# watch 'zpool list; echo; zfs list'
# watch zfs get compressratio -o all
# watch cat /proc/spl/kstat/zfs/arcstats

If you have a scrub or resilvering in progress you can report on progress with:

# watch zpool status -v

You can poke about in internals, e.g.:

# cat /proc/spl/kstat/zfs/arcstats
root@orac:/sys/module/zfs/parameters# tail *

You can report on property values with e.g.:

# zfs get all data

If you want to get funky:

# cd /tmp
# perf record -ag #(Ctrl+C after ~15 seconds)
# perf report --stdio

You can search for ZFS files like e.g. this:

root@orac:/# find / -name '*zfs*' -or -name '*zpool*'

You can report history of a zpool:

# zpool history $poolname

You can get a report on the dedup tables:

# zpool status -D $poolname

Or more detailed dedup table info:

# zdb -DDD $poolname

Note in the output see here for details, basically:

Abbr Description
LSIZE logical size (in memory)
PSIZE physical size
DSIZE size on disk
refcnt reference count

How to tell if zfs scrub is running

You can get the status from the "scan:" line from:

$ zpool status

Measure data throughput

Use the 'pv' command from the 'pv' package, e.g.:

# cat /dev/sda | pv | cat > /dev/null

Or for ZFS:

# zfs send data/example | pv | cat > /dev/null

Using Smartctl, Smartd and Hddtemp on Debian

For notes on using smartctl see Using Smartctl, Smartd and Hddtemp on Debian.

Report hard disk usage

So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.

Report hard disk temperatures

E.g.

# hddtemp /dev/sd[a-e]

Burning an ISO image to USB on Mac

First insert your USB key and find the appropriate disk with:

# diskutil list

Then unmount it with:

# diskutil unmountDisk /dev/disk4

Then copy ISO image with 'dd':

# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4

You can get dd to report progress by sending it the SIGINFO signal:

# kill -s info 12345

Listing all ext4 file systems

To see a list only of the mounted ext4 file systems:

# df -t ext4

Report hierarchical file system mount points and mount options

$ findmnt

Report the mount point for the current working directory

$ findmnt "$PWD"

Monitoring disk I/O

There's an app for that! iotop.

Using iotop, top for disks

# iotop -oPa

Monitor disk I/O for performance issues

# watch iostat

Or e.g.

# watch iostat -xd /dev/sd[abc]

Or use groupings like this command for 'tact':

$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2

Monitoring a system

Simple ZFS monitoring

# watch iostat
# iotop
# zpool iostat -v 5
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
# nethogs
# top

Monitoring temperature

See temperature without third-party apps for:

$ cat /sys/class/thermal/thermal_zone*/temp

and:

$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'

Monitoring CPU temperature

$ watch sensors

Monitoring HDD temperature

For e.g. SATA drives sda to sdd:

# watch hddtemp /dev/sd[a-d]

ZFS

How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

See How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

$ cat /proc/spl/kstat/zfs/arcstats

Then:

c is the target size of the ARC in bytes
c_max is the maximum size of the ARC in bytes
size is the current size of the ARC in bytes

Stopping a ZFS scrub in progress

# zpool scrub -s $pool

e.g. for the 'data' pool:

# zpool scrub -s data

File management

Listing files by size

Use capital S for Size:

$ ls -S

Listing only directories

$ ls -l | egrep '^d'

Listing only files

$ ls -l | egrep -v '^d'

Listing hidden files

$ ls -al .[!.]*

Creating a symbolic link

$ ln -s /path/to/target link-name

Creating a hard-link

$ ln /path/to/target file-name

Changing the owner of a file

$ chown user:group <files>

E.g.

$ chown jj5:staff README
$ chown root:root *

To apply recursively into sub-directories use -R,

$ chown -R root:root /etc/*

Changing file permissions

Object codes
User Group Other
u g o
Permission codes
Read Write Exectue
r w x
4 2 1
Numeric codes
0 None
1 Execute
2 Write
3 Write, Execute
4 Read
5 Read, Execute
6 Read, Write
7 Read, Write, Execute

See Numeric Mode in Action.

$ chmod <user numeric code><group numeric code><other numeric code> <files>
$ chmod <object codes>+|-<permission codes> <files>

E.g.

$ chmod 600 my-private-file
$ chmod go-rwx my-private-file
$ chmod u+rw my-private-file
$ chmod +x my-script

Updating config files

If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:

$ cp old.conf updated.conf
$ merge -A updated.conf new.conf old.conf

Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.

The merge program is a part of the RCS package. If you don't have it:

$ sudo apt-get install rcs

Listing open files

Use lsof to list open files. E.g.:

# lsof

See man lsof for options.

List permissions on a whole directory path

E.g.:

$ namei -om /home/jj5/workspace

Outputs:

f: /home/jj5/workspace/
 drwxr-xr-x root root /
 drwxr-xr-x root root home
 drwxr-xr-x jj5  jj5  jj5
 drwxr-xr-x jj5  jj5  workspace

Counting non-blank lines in a file

E.g.:

$ cat foo.c | sed '/^\s*$/d' | wc -l

Cloning one directory to another with rsync

E.g.:

rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/

Counting number of files in current directory and all subdirectories

$ ls -AlhR . | egrep '^-' | wc -l

Counting number of directories in current directory and all subdirectories

$ ls -AlhR . | egrep '^d' | wc -l

Getting the status of a 'dd' process

First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'

Then send the dd process the SIGINFO signal, which for dd process 40947 would be:

# kill -s info 40947

The dd process will report its status in the terminal its running in.

Transferring a large file via FAT32 file system

So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:

$ split -b 4000m input.tgz input.tgz-parts-

Then copy the small files and reassemble:

$ cat input.tgz-parts-* > output.tgz

Find the difference between two directories

$ diif -qr $DIR_A $DIR_B

Merging two directories

$ cp -RT source/ destination/

Files from source will be merged into destination.

Generating a replacement file

So you generate the file into a temp file, then hard link the temp file to where you want the replacement to go, then you delete the temp file:

$ generate-file.sh > file.txt.tmp
$ ln -f file.txt.tmp file.txt
$ rm file.txt.tmp

NFS

List NFS shares

To e.g. show NFS shares on 'love':

$ showmount -e love

Compression

How to use pigz with tar

See here:

$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz

Note: don't use --best unless you're being stingy, running without it will be much faster.

Also from here:

Fast pack:

tar -I 'pigz --fast' -cf my.tar.gz whatver

Best pack:

tar -I 'pigz --best' -cf my.tar.gz whatver

Fast unpack:

tar -I pigz -xf my.tar.gz

Best compression with tar

From here:

export GZIP=-9
tar cvzf file.tar.gz /path/to/directory

or

env GZIP=-9 tar cvzf file.tar.gz /path/to/directory

Best parallel compression with pigz

$ pigz --best

Best parallel compression with xz

$ xz -9e -T 0

Reporting compression ratios with xz

e.g.

root@love:/data/image/archive# xz -l *
Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
    1       3    372.2 MiB    442.3 MiB  0.841  CRC64   1999.txz
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64   2001.txz
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64   2002.txz
    1       9    568.5 MiB  1,660.2 MiB  0.342  CRC64   2003.txz
    1     639     66.8 GiB    119.6 GiB  0.558  CRC64   2004.txz
    1     313     12.7 GiB     58.6 GiB  0.217  CRC64   2005.txz
    1     414     35.0 GiB     77.4 GiB  0.452  CRC64   2006.txz
    1     485     44.5 GiB     90.9 GiB  0.490  CRC64   2007.txz
    1   1,690    150.0 GiB    316.8 GiB  0.473  CRC64   2008.txz
    1       3    457.9 MiB    526.0 MiB  0.871  CRC64   2009.txz
    1     168     27.3 GiB     31.4 GiB  0.868  CRC64   2010.txz
    1       4    477.1 MiB    702.8 MiB  0.679  CRC64   2011.txz
-------------------------------------------------------------------------------
   12   3,768    344.6 GiB    705.5 GiB  0.488  CRC64   12 files

Symbolic-link management

== Data used by sym-linked files:

This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:

jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h

File searching

Finding a file with a particular name

$ find -iname "*some-part-of-the-file-name*"

Will start searching from the current directory, so maybe

$ cd /

first. For a case-sensitive search:

$ find -name "*eXaCT CaSE*"

Finding a file with particular content

To search in /etc/ for a file with particular content:

$ grep -R "search-string" /etc/*

To search the current directory for *.cs files containing the word "Up":

$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;

Finding a list of files with particular content

E.g. to find all the files with the word 'creativity':

$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq

Using the locate command to find files

$ locate part-of-filename

E.g.

$ locate texvc

Updating locate command's database

# updatedb

Select a random line from a text file

$ shuf -n 1 input.txt

Extra context for grep

If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:

$ grep -B 3 -A 1 ...

Job control

Stopping a running process

Press Ctrl+Z to stop a running process.

Listing current jobs and their status

$ jobs

Resuming a stopped job in the backgroud

To resume a stopped process in the background

$ bg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Resuming a stopped job in the foreground

To resume a stopped process in the foreground

$ fg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Killing a stopped job

To kill a job

$ kill %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Periodically run a program and watch its output

$ watch /your/command

Debian/Ubuntu package management

Also see Where "is" it? on the Debian Wiki.

configuring debconf

# dpkg-reconfigure debconf 

Set priority to low to get asked detailed questions.

Showing list of installed packages

# dpkg --get-selections

Searching for installed package

# dpkg --get-selections | grep package-name

or

# aptitude search package-name

Showing which files are installed as part of a package

# dpkg -L package-name

Installing a package

# apt-get install package-name

Uninstalling a package

# apt-get remove package-name

Showing system architecture

$ dpkg --print-architecture

Showing which package a file belongs to

$ which echo
/bin/echo
$ dpkg -S /bin/echo
coreutils: /bin/echo
$ dpkg -l | grep coreutils
ii  coreutils                         6.10-6                   The GNU core utilities

Showing package information

$ apt-cache showpkg coreutils

Or for even more information:

$ apt-cache show coreutils

List all installed packages with package version info

dpkg-query -l

Reporting which version of a package is installed

$ dpkg -l | grep package-name

E.g.:

root@hope:~/letsencrypt# dpkg -l | grep augeas
ii  augeas-lenses                   0.7.0-1ubuntu1                 Set of lenses needed by libaugeas0 to parse 
ii  libaugeas0                      0.7.0-1ubuntu1                 The augeas configuration editing library and

Comprehensive upgrade

Try the following:

# apt-get update
# apt-get dist-upgrade
# apt-get autoremove
# apt-get remove $(deborphan)
# update-flashplugin-nonfree --install

Searching all available packages

$ apt-cache search . | sort -d | less

Reporting unattended upgrades status

See here for more info.

# tail -f /var/log/unattended-upgrades/unattended-upgrades.log

Searching for Debian packages and versions

Networking

Determining throughput between two hosts

# apt install iperf3

On the server:

# iperf3 -s

On the client:

# iperf3 -c $SERVER_IP

For more info see: How to test the network speed/throughput between two Linux servers.

net-tools vs iproute2

The older 'net-tools' package has been replaced with 'iproute2' e.g. in stretch.

legacy net-tools commands iproute2 replacement commands
arp ip n (ip neighbor)
ifconfig ip a (ip addr), ip link, ip -s (ip -stats)
iptunnel ip tunnel
iwconfig iw
nameif ip link, ifrename
netstat ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
route ip r (ip route)

Restart networking

For servers:

# service networking restart

For desktops:

# service network-manager restart

Pinging with particular packet size

$ ping -M do -s <packet size in bytes> <host>

E.g.

$ ping -M do -s 1400 charity.progclub.org

Setting MSS for a particular IP address on a particular interface

# ip route add <host> dev <interface> advmss <packet size>

E.g.

# ip route add 10.0.0.1 dev eth0 advmss 1400

Dropping configured MMS for a particular IP address

# ip route flush <host>

E.g.

# ip route flush 10.0.0.1

Listing open ports and socket information

Including which process is listening on which port.

# netstat -tulpn

Or use the 'ss' command:

# ss -s
# ss -l
# ss -pl
# ss -o state established '( dport = :smtp or sport = :smtp )'

Listing open IPv4 connections

# lsof -Pnl +M -i4

You might need to install the lsof package:

# apt-get install lsof

Query for DNS MX record

$ nslookup
> server 127.0.0.1
> set q=mx
> mail.blackbrick.com

Query for DNS SOA record

$ dig @ns2.staticmagic.net -t SOA staticmagic.net

Using nmap to list open ports on remote host

To check the 1,000 most common ports:

# nmap server.example.com

Or for a specific port range (e.g. 101 to 102):

# nmap -p 101-102 server.example.com

Or for all ports (1 to 65,535):

# nmap -p- server.example.com

Network monitoring

See here for details. Basically:

  1. Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
  2. Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
  3. Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
  4. Bandwidth per process: nethogs

nload

You can watch network traffic in real-time with nload:

# nload -u M

Reporting network (NIC) speed

From here:

# dmesg | grep eth0
# mii-tool -v eth0
# ethtool eth0

Note: use ifconfig to get device name.

Path MTU discovery

To do a Path MTU Discovery, from the iputils-tracepath package:

# tracepath host.example.com

Listing available Ethernet devices

To see a list of NICs available on the host:

$ cat /proc/net/dev

Also

$ ip link

59 Linux Networking commands and scripts

See 59 Linux Networking commands and scripts.

Links

IPTables

Applying firewall rules

For configuration info see this article.

$ sudo vim /etc/iptables.test.rules
$ sudo /sbin/iptables -F
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
$ sudo iptables -L
$ sudo -s
# iptables-save > /etc/iptables.up.rules
# exit

Blocking an IP address with iptables

To drop IP address 1.2.3.4:

# iptables -A INPUT -s 1.2.3.4 -j DROP

ufw

Denying hosts with ufw

See denying hosts with ufw.

Bind9

Viewing Bind9 querylog

$ sudo rndc querylog
$ tail -f /var/log/syslog

IPSec

Disabling IPSec

# setkey -FP

OpenSSL

Debugging IMAPS with OpenSSL

# openssl s_client -connect localhost:993
> a1 LOGIN username@host password
> a2 LOGOUT

Debugging HTTPS with OpenSSL

$ openssl s_client -connect www.example.com:443
GET /example.html HTTP/1.1
host: www.example.com

Links

Pluggable Authentication Modules (PAM)

Links

SSH

Configuring SSH key login

On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):

$ ssh-keygen -t rsa

Copy the public key from the client to the server:

$ scp ~/.ssh/id_rsa.pub user@example.org:

Configure the authorized keys on the server:

$ ssh user@example.org
$ mkdir ~/.ssh
$ chmod go-w .ssh
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ rm ~/id_rsa.pub

Tunneling over SSH

For example, connecting a remote MySQL server to the localhost:

$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org

If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,

 $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au

The -L stanza is localport:remotehost:remoteport where localport is a port on your machine, forwarded to remoteport on remotehost.

Tunneling over SSH with PuTTY

See Connecting to the MySQL database remotely (via an SSH Tunnel)

  • run putty.exe
  • Connection -> SSH -> Tunnels
    • Port forwarding: source port to 3306
    • destination: 127.0.0.1:3306
    • check Local
    • click Add

Enabling verbose SSH logging

To see what's going on with your ssh connections,

$ ssh -v user@host

Or

$ ssh -vv user@host

Unlocking SSH key for session

jj5@orac:~/.config/autostart$ cat ssh-add.desktop 
[Desktop Entry]
Type=Application
Name=ssh-add
Comment=Adds my private key to my session.
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'

Links

Standard IO

cat EOF

$ cat > output <<EOF
> text
> EOF
$ cat output
text

Script

Creating a session log with script

$ script -t 2> timing

The session log is in the file 'typescript' and the timing data is in 'timing'.

Replaying a scripted session

$ scriptreplay timing

Uses the default file 'typescript' and the 'timing' file as specified.

Screen

Creating a new screen or reconnecting to a detached screen

$ screen -R

Detaching a screen

$ screen -D

Reconnecting to screen

$ screen -D
$ screen -R

I have a script in ~/bin/reconnect like so,

#!/bin/bash
screen -D
screen -R

This will detach your last screen, and reconnect it on the current terminal.

Scrolling in screen

See How to scroll in GNU Screen. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.

tmux

Live collaboration with tmux

User A:

tmux -S /tmp/collab
chmod 777 /tmp/collab

User B:

tmux -S /tmp/collab attach

Vim

First, why Vim?

Read Why, oh WHY, do those #?@! nutheads use vi?

Visual modes

Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.

Configuring spaces instead of tabs

I use two spaces instead of tabs. To configure, edit your .vimrc file:

$ vim ~/.vimrc

and include the following lines:

set tabstop=2
set shiftwidth=2
set expandtab

Configuring syntax highlighting

See here.

Use:

:syntax on

to turn on syntax highlighting.

Use:

:syntax off

to turn off syntax highlighting.

To always use syntax highlighting:

$ vim ~/.vimrc

and add:

syntax on

To get a list of supported colour schemes open vim and type:

:colorscheme[space][Ctrl+D]

To always use a particular colorscheme edit ~/.vimrc and add (for example):

colorscheme desert

Inserting a TAB character when expandtab is on

The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.

Press Ctrl+V TAB to insert a literal tab character.

Or you can disable tab expansion altogether with:

:set expandtab!

Changing 2 space indent to 4 space indent (e.g. for python files)

:%s/^\s*/&&/g

For more information see here.

Recording and replaying a macro

To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".

Deleting to end of line

d$

Deleting to beginning of line

d^

Finding text

To search forward for "text":

/text

To search backward for "text":

?text

To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.

Finding and replacing text

To replace the first instance of "search" on the current line with "destroy":

:s/search/destroy/

To replace all instances of "search" on the current line with "destroy":

:s/search/destroy/g

To replace all instances of "search" on lines 13 to 37 with "destroy":

:13,37 s/search/destroy/g

To replace all instances of "search" in the entire file with "destroy":

:%s/search/destroy/g

Changing DOS/Windows line-endings (CRLF) to Unix line-endings

To set the line-ending to Unix line endings run the command:

:setlocal ff=unix

More information on managing file formats available here.

Disabling auto-indent etc. to paste from clipboard

To disable smart indenting when you're going to paste in text:

:set paste

To turn it off again:

:set nopaste

There's more info in this article: Toggle auto-indenting for code paste

Positioning windows

Use -o for horizontal split, e.g.:

vim -o a.txt b.txt

Use -O for vertical split, e.g.:

vim -o a.txt b.txt

Use ^W to navigate windows then use directional keys h, j, k, l, etc.

Use ^W and < or > to resize windows.

To indent a block of text in Vim

Use the > command. E.g. to indent five lines:

5 > >

Press . (dot) to keep indenting.

Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:

> %

See here for more.

Open a file in a new window/tab

To open a file on the left hand side:

:vert new filename.ext

Note: ':vnew filename.ext' and ':vsp filename.ext' also work.

To open a file at the top:

:new filename.ext

See here for more.

Explore files in Vim

Enter:

:Explore

Switch between Vim tabs

Use gt and gT.

Switch between Vim windows

To toggle between open windows use:

Ctrl+W W

To move in a direction use:

Ctrl+W h/j/k/l

See here for more.

Insert block comment in Vim

See here for line-commenting.

So it's:

  1. Ctrl+V (Note: not Shift+V!)
  2. Up/Down to select rows
  3. Shift+I
  4. Enter your text, e.g. '#' or '//'
  5. Ctrl+[ (or 'Esc')

Navigate to matching tag

To navigate to the matching beginning or end tag use '%'.

You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.

Auto-format HTML tags

Stolen from here.

  1. first join all the lines - ggVGgJ
  2. Now break tags to new lines - :%s/>\s*</>\r</g
  3. Now set filetype - :set ft=html (you can do this before too)
  4. Now Indent - ggVG=

Links

Create PDF from text using Vim

Generate PDF from input.txt with:

$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps

Examine output with:

$ okular doc.pdf

Write

Talking to other users on the system

write is a unix command for talking to other users on the system. To use write:

1. SSH to <username>@<hostname> and login with your username and password.

2. Issue the following command to find out who is logged onto the system:

$ who

3. Issue the following command to talk to a specific user:

$ write <username>

4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.

Date

Reporting the time on the server

$ date

Reporting UTC time

$ date --utc

Getting the date in yyyy-MM-dd-hhmmss format

$ date="`date +%F-%H%M%S`"

Getting the year in four digits

$ year="`date +%Y`"

Getting the month in two digits

$ month="`date +%m`"

Getting the day of the month in two digits

$ day="`date +%d`"

Getting yesterday's date

$ date --date='1 day ago' +%Y-%m-%d

Converting Unix time (seconds since epoch)

For timestamp '1501370200':

$ date -d @1501370200 +%F-%H%M%S

Running timedatectl from systemd

There's a new command bundled with systmed:

# timedatectl

It reports on (and controls) how the system time is configured.

MySQL (and MariaDB)

Run mysql without authentication/authorisation

# service mysql stop
# mysqld_safe --skip-grant-tables &

Then you can connect without a password, e.g.:

# mysql -u root mysql

To stop the unauthenticated service:

# mysqladmin shutdown

Then restart a normal service:

# service mysql start

Logging all database queries

# vim /etc/mysql/my.cnf

In the [mysqld] section add:

log=/tmp/mysql.log

Then:

# service mysql restart

Watch the log with:

# tail -f /tmp/mysql.log

Or:

SET GLOBAL log_output = 'FILE';
SET GLOBAL general_log_file = 'my_logs.txt';
SET GLOBAL general_log = 'ON';

my_logs.txt will be in /var/lib/mysql

Dumping a MySQL database

You can dump the database into a file using:

$ mysqldump -h hostname -u user --password=password databasename > filename

Loading a MySQL database from a dump file

You can create a database using:

$ echo create database databasename | mysql -h hostname -u user -p

You can restore a database using:

$ mysql -h hostname -u user --password=password databasename < filename

Creating a MySQL user

# mysql -h localhost -u root --password=<password>
mysql> create user 'username'@'localhost' identified by '<password>';

Granting all MySQL user permissions

# mysql -h localhost -u root --password=<password>
mysql> grant all privileges on dbname.* to user@host;

Select domain name from email address

SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )

Check if MySQL connection is encrypted with TLS/SSL

Check the SSL version in use:

show status like 'Ssl_version';

Or check the cipher in use:

show status like 'Ssl_cipher';

Report on server config

See SHOW Statements for the full list, but check out:

SHOW VARIABLES

and

SHOW STATUS

and

SHOW PROCESSLIST

Monitor MySQL activity

$ watch "mysql -t -e 'show processlist'"

Apache

Reporting loaded Apache modules

# apache2ctl -M

Maintaining .htaccess passwords

To add or modify the password for a user:

$ htpasswd /etc/apache2/passwd username

Configuring PHP session timeout in .htaccess

For a session timeout of 9 hours:

php_value session.cookie_lifetime 32400
php_value session.gc_maxlifetime 32400

Disabling PHP magic quotes in .htaccess

php_flag magic_quotes_gpc Off

Requiring HTTP Auth in .htaccess

AuthType Basic
AuthName "Speak Friend And Enter"
AuthUserFile /home/jj5/.htpasswd
Require valid-user

Restarting Apache

The hard way

$ sudo /etc/init.d/apache2 restart

The graceful way (avoids dropping active connections)

$ sudo apache2ctl graceful

Allowing directory browsing

To show directory index pages, in the apache config file:

<Directory /var/www/data>
  Options Indexes
</Directory>

C

Locating memset function

The memset function is in <string.h> as described in this article Using memset(), memcpy(), and memmove() in C

Links

PHP

Including a file relative to the including file

require_once( dirname( __FILE__ ) . '/relative/path/to.php' );

Enabling error reporting

error_reporting( E_ALL | E_STRICT );
ini_set( 'display_errors', 'On' );

Setting an error handler

set_error_handler( "error_handler", E_ALL | E_STRICT );
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
  // ...
}

Disable HTML content in var_dump

ini_set( 'html_errors', 'off' );

Report PHP modules

$ php -m

PHP Security Best Practices For Sys Admins

See Linux 25 PHP Security Best Practices For Sys Admins.

BASH scripting

For a primer on bash scripting see TFM: Erotic Fantasy: /bin/sh Programming.

Telling a script to run in bash

The first line of the file should be:

#!/bin/bash

Checking if a command-line argument was passed in

if [ -n "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking if a command-line argument was not passed in

if [ "$1" = "" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Or:

if [ -z "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking command exit status

cd /my/path
if [ "$?" -ne "0" ]; then
  echo "Cannot change dir.";
  exit 1;
fi

Checking if a file does/doesn't exist

Check if file exists:

if [ -f "/my/file" ]; then
  cat /my/file
fi

Check if file doesn't exist:

if [ ! -f "/my/file" ]; then
  touch /my/file
fi

Checking if a directory does/doesn't exist

Check if directory exists:

if [ -d "/my/dir" ]; then
  rmdir /my/dir
fi

Check if directory doesn't exist:

if [ ! -d "/my/dir" ]; then
  mkdir /my/dir
fi

Deleting old backups

To keep only the latest five backups:

find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f

This script stolen from stackoverflow.

Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.

Changing into the script's directory

cd "`dirname $0`"

Getting the absolute path of a relative path

readlink -f ./some/path

Creating a temp directory

dir=`mktemp -d` && cd $dir

Reading secret input from stdin

You can read a secret, such as a password, like this:

echo -n "Enter passphrase: "
stty -echo
read passphrase;
stty echo
echo ""

After running the above the secret will be in the $passphrase environment variable.

String replacements in bash

See the string manipulation doco. Basically, to replace first occurrence:

result=${var/find/replace}

To replace all occurrences:

result=${var//find/replace}

A practical example, get an ISO date and turn it into a path:

date="$(date +%Y-%m-%d)"
work_dir=${date//-//}

Sending a HEREDOC to a file

cat << EOF > /tmp/yourfilehere
These contents will be written to the file.
        This line is indented.
EOF

Bash case/switch statement

See using case statements, e.g.:

case $space in
[1-6]*)
  Message="All is quiet."
  ;;
[7-8]*)
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
  ;;
9[1-8])
  Message="Better hurry with that new disk...  One partition is $space % full."
  ;;
99)
  Message="I'm drowning here!  There's a partition at $space %!"
  ;;
*)
  Message="I seem to be running with an nonexistent amount of disk space..."
  ;;
esac

Using dotglob shopt to match dot-files

To enable dot-file matching in globs, set the dotglob shell option:

$ shopt -s dotglob

Stopping a script from running if it previously exited due to error

persistentDataDir=/var/lib/something
alarm() {
  touch $persistentDataDir/alarm
}
trap alarm ERR
[ -f $persistentDataDir/alarm ] && exit 1

Make sure only one instance of a script is running at a time

ephemeralDataDir=/var/run/something
unlock() {
  rmdir $ephemeralDataDir/lock
}
mkdir $ephemeralDataDir/lock || exit 1;
trap unlock EXIT

BASH programming advice

See Anybody can write good bash (with a little effort).

Run a command using arguments that come from an array

See here:

#!/bin/bash
tabs=("first tab" "second tab")
args=()
for t in "${tabs[@]}" ; do 
  args+=(-t "$t")
done
app "${args[@]}"

Display a CSV in columnar or tabular format

$ column -t -s , data.csv

Maximum command line length

Technically this is an operating system limit, not a BASH limit.

$ getconf ARG_MAX    # Get argument limit in bytes/chars

Sed

Find and replace with sed

To update the current file use '-i'. E.g.:

sed -i 's/search-text/replace-text/' file

Awk

Listing IP addresses in an Apache web log

awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq

Printing space-separated field

echo 'no no yes no' | awk '{print $3}'

Printing delimited field

echo 'no:no:yes:no' | awk -F ':' '{print $3}'

Subversion

Setting svn:externals from the command-line

See here.

To set an svn:externals from the command-line:

svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
svn ci -m 'Adding svn:externals for rdfind-php...'
svn up

Or to use a file:

svn propset svn:externals -F svn.externals .

Setting svn:ignore from the command line

See here.

$ svn propset svn:ignore [file|folder] [path]

Or use a file and apply recursively:

$ svn propset svn:ignore -RF ./svn-ignore-list.txt .

Git

Showing status of working copy

git status

Showing repo history

git log

Showing remote repositories (including 'origin')

git remote -v

Handy git aliases

Save these to your ~/.gitconfig file.

For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:

 graph = !git log --all --graph --color --abbrev-commit --pretty=oneline

To show only the files that have changed, rather than the full line-by-line content:

 dif   = !git diff --name-status

Show git remote URL

git config --get remote.origin.url

IRC

Instructing ChanServ to op an admin

/msg ChanServ op #channel user

E.g.

/msg ChanServ op #gnurc jj5

Sub 'op' for 'deop' to remove op privilege.

C++

C++ books

Books I want

Books I own

Books I'm not reading

Books I've read

C++ blogs/articles

C++ performance tips

  • ++c can be faster than c++.
  • use const for everything that you possibly can.
  • use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
  • don't use registers.
  • const rarely affects performance.
  • debunking a number of C++ myths that won't die.
  • std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
  • if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
  • read about performance cost of RTTI (Run Time Type Information) and how to disable it
  • don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
  • prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
  • Which is better, static or dynamic linking?
  • Integer vs Floating-Point performance

systemd

systemd is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.

Following a service log

e.g. for bind9:

# journalctl -f -u bind9

or for everything:

# journalctl -f

System status

To see spawned services hierarchy:

# systemctl status

Or for a specific service e.g.:

# systemctl status networking

SaltStack

Running a command on specified minions

From the salt master:

salt 'host' cmd.run 'update-locale'

From the salt minion:

salt-call cmd.run 'update-locale'

Running a command on all minions

salt '*' cmd.run 'update-locale'

Running a specific state file

From the salt master:

salt $MINION_ID state.sls $STATE_FILE

From the salt minion:

salt-call state.sls $STATE_FILE

Listing active jobs

salt-run jobs.active

Listing available grains

salt 'example' grains.items

Listing available pillar

salt 'example' pillar.items

Reporting a grain value

e.g. for the 'mem_total' grain:

salt '*' grains.item mem_total

Passing a variable into a Jinja template from a salt state (SLS)

e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:

/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:
  file.managed:
    - template: jinja
    - user: root
    - group: root
    - mode: 644
    - source: salt://file/srv/zabbix/release/source.txt
    - require:
      - file: /srv/zabbix/release
    - default:
      zabbix_deb_pkg: {{ zabbix_deb_pkg }}
      zabbix_deb_url: {{ zabbix_deb_url }}

KDE

Running user login script (X11/XOrg/XWindows)

A way to run user login scripts which works for KDE Plasma (and apparently other X.Org Server X Window System environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:

[Desktop Entry]
Type=Application
Name=ssh-add
Comment=Adds my private key to my session.
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'

Standard KDE shortcut key bindings

Name Shortcut Command
Send Ctrl+D Pause xdotool key "ctrl+d"
Insert comment F1 xdotool type "$(date +%Y-%m-%d ) $USER - "
Insert sydtime F4 xdotool type "$(date +%Y-%m-%d-%H%M%S)"
Konsole Meta+T konsole
Dolphin Meta+E dolphin
Firefox ScrollLock firefox
Kate Ctrl+Shift+F12 kate
KCalc Ctrl+Shift+F11 kcalc

Shutting down KDE/Plasma

# /etc/init.d/sddm stop

VirtualBox

Mounting a VirtualBox VDI file

Note: instead of doing this consider booting with a live CD.

See here:

Install qemu if necessary:

# apt install qemu

Then you'll need to load the network block device module:

# rmmod nbd
# modprobe nbd max_part=16

Attach the .vdi image to one of the nbd you just created:

# qemu-nbd -c /dev/nbd0 drive.vdi

Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.

# mount /dev/nbd0p1 /mnt

Once you are done, unmount everything and disconnect the device:

# qemu-nbd -d /dev/nbd0

Elasticsearch

Report on health of your Elasticsearch cluster

$ curl http://localhost:9200/_cluster/health?pretty

Zabbix

Zabbix Agent on Mac OS X

Download and install agent.

Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf

Unload agent with:

# launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

Load agent with:

# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

To add a 'pki' group:

# dseditgroup -o create pki

To monitor syslog on Mac OS X:

# tail -f /var/log/system.log

Installing Zabbix Agent from source on Mac OS X

Download sources from https://www.zabbix.com/download_sources

$ brew update
$ brew install openssl
$ brew install pcre
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install

NetBeans

NetBeans shortcut keys

Keys Action
Ctrl+W Close active window
Alt+Shift+K Open in Terminal
Ctrl+U U Convert selected text to uppercase
Ctrl+U L Convert selected text to lowercase

XML

How to pretty-print an XML file

$ xmllint --format input.xml > output.xml

ApacheBench

Run a benchmark with ApacheBench

$ ab -n 1000 -c 100 https://www.example.com/